If you're already sharing content with a friend, you can edit the sharing information whenever you like.
Open Plex Web App to Access Users
You can access these under Settings > Users in Plex Web App.
Click the Friends menu option on the left to access your Friends.
Alternatively, you can also access the Users item under the Account dropdown at the top right.
Related Page: Plex Media Server > Using Plex Web App
Edit a Friend
Select a Friend to Edit
Click the edit (pencil) icon for a friend to edit that entry.
A window will appear to allow you to edit that friend.
The General tab shows the email address for the friend's account and also allows you to remove the friend.
On the left, you'll see a list of Plex Media Servers associated with your Plex account. For each Server, you can choose whether or not to share content with the friend.
You can leave All Libraries selected or you can unselect it to choose only individual Libraries to share.
Restrictions allow you to more finely control access to content you share. You can choose whether or not the friend is able to sync shared content, use Camera Upload, or access channels. You can also select specific content ratings from your Library to share as well as content that you've set with a specific Label.
Tip!: Restrictions beyond Allow Channels require an active Plex Pass subscription for the main Plex Media Server account.
Related Page: Cloud Services > Server Sharing > Restricting the Shares
Remove a Friend
If you wish to remove the friend altogether, you can do that, too.