Hi there, and welcome to PRO!
Yes, you can. You can use the following command:
/friend <username> | /fri <username> Usage: Sends a friend request to <username>.
Using the command on a friend who is online will remove <username> from your friend's list.
You can find a list of All Available Commands following this link. Please note that the user needs to be online for you to add them to your friend list.
You can also click on them, or their name in chat, and use the "Friend/Unfriend" option, although on smaller screens it may be wiser to use the aforementioned command to avoid hitting another option on that list instead.
Since the matter is already fully covered, I will now lock this topic; I wish you to have a nice day!
- Locked -