There are several scenarios here depending on what you actually want to do with your assets.
How can I delete an asset from the Pics.io library?
If you want to delete your asset from the entire Pics.io library, you just need to hit the trash bin icon on the left side panel, in the Details panel, or on the thumbnail of the asset. Read more about deleting files from Pics.io here.
How can I remove assets from a collection?
If you simply want to remove an asset from one particular collection/Lightboard, but keep it in all other places in the Pics.io library, you need to use the Remove from collection button. To do so, just open your asset and find the Collections section in the Details panel. Choose a collection you want to remove the asset from and click on the cross button next to its name.
Alternatively, you can do the same on the thumbnail of your file, by clicking on the Remove from collection button on the thumbnail of the asset. In this way, you will remove this asset from this particular collection, but save it in all other collections or lightboards it may belong to.
The other way to remove one asset from a particular collection is click on the Remove from collection button on the bottom toolbar:
NB! The Remove from collection button is only available when one asset is selected. If you've selected multiple assets, please use the Details panel on the right side of the screen to remove assets from secondary collections.
Please note that if the removed asset belonged to only one collection, it will be moved to the root folder. You can find it later with the help of the "Don’t show assets in nested collections" button in the bottom of the collections tree.
How can I remove several assets from a collection in bulk?
If you want to remove multiple assets in one click, you should first select them, open the Details panel, and click on the cross next to the name of the collection.
Please note that an original asset can be reflected in the multiple Pics.io collections spontaneously. It doesn't mean that the second asset is a duplicate, two of them are related to a single file in your storage. Thus, make sure that you check local permissions. Deletion of a file from one collection triggers the deletion of this asset from both locations.
Removing assets from lightboards has some peculiarities. You can read more about it here.
How can I delete a collection?
In case you want to delete an entire collection, simply mouse over the collection you wish to delete and click on the "Delete collection" button. You will be provided with two options for what to do with the assets inside this collection. This is especially useful if the assets from this collection were also added to other collections in Pics.io:
Remove from this collection only - The assets will be removed only from this collection but will remain in any other collections they are added to.
Delete from all collections - The assets will be removed from all collections they are added to throughout the library.
What will happen to assets on the storage side?
As you may know, adding assets to different collections means displaying them in multiple collections inside Pics.io interface, while keeping only one original file in one corresponding collection inside your Google Drive or S3 storage.
So, if the original assets on the storage side are located inside the collection that you are going to delete, upon removing them from this collection, such assets on the storage side will be moved to another collection where they have been added to inside Pics.io interface.
Here's a detailed example:
Imagine you have Collection A with the original asset on the storage.
On the Pics.io side, this original asset lives inside Collection A, but also in Collections B, C, etc., because it was added to those collections in Pics.io.
On the Pics.io side, you want to delete Collection A and choose the option for assets to "Remove from this collection only."
Collection A is deleted in Pics.io and on the storage along with the assets inside it.
On the storage side, the original asset that belonged to Collection A will be moved to the collection where it was added in Pics.io. If the asset was added to multiple collections, then it will be moved to the one where it was added first (in this case, Collection B).
So in summary, upon deleting Collection A with the option "Remove from this collection only.", on the storage side, be it Google Drive or Amazon S3, this asset will be moved to Collection B.
Here you may find more information about how to manage your collections.