Once you've created a collection in your Library, you can manage or delete it in the following way:
iOS
1. Open the desired collection.
2. Tap on the three dots at the top right corner of the screen.
3. A window will open where you'll find the options "Rename collection" or "Delete collection". Tap on the first one to change the name of your collection, and on the second one to remove it from your Library.
You can also remove a title from your collection:
1. Open the collection, find the title you'd like to remove and tap on the three dots next to it.
2. You can remove the title from that collection by tapping on "Remove from...", or you can save it to a different one by tapping on "Save to a collection".
Finally, by tapping on the down-arrow next to "Sort by", underneath the title of a collection, you'll be able to sort the titles in the collection according to your preferred criteria.
Android
1. Open the collection you'd like to edit or delete.
2. Tap on the three dots at the top right corner of the screen.
3. A window will open where you'll find the options: "Rename the collection" or "Delete collection". Just tap on your preferred one.
You can also remove a title from your collection:
1. Open the collection, find the title you'd like to remove and tap on the three dots next to it.
2. You'll find the option to remove the title from that collection by tapping on "Remove from..." or to save it to a different one by tapping on "Save to a collection".
