First, you will want to navigate to the Collections Settings. You can do so by going to the Collection and clicking the gear icon.

Or by clicking your profile picture in the top right corner > click "Admin" > scroll to the "Navigation and Spaces" heading > click "Collection List" > hover over the Collection you'd like to change the name for > click "Manage Collection". A Collection name can be up to 40 characters long.

You can also hover over the Collection in the left-hand navigation and select the three-dot menu > "Manage Collection".

And choose a new name for your Collection!

To learn how to manage your Collection settings, check out “How Do I Manage My Collections?