Hi,
if you want to remove a user from your friend list entirely:
1) open your friend list
2) tick the box to the left of said user
3) scroll to the bottom and click 'Delete'
If you are looking to keep them in your friend list but change the sorting in your friend list:
1) open your friend list
2) tick the box to the left of all users you want to change in their sequence
3) assign numbers in the box, the higher the number is, the higher the person is displayed in your friends list. For example: if you put the number "6" next to one friend and "5" next to another one, the user assigned with 6 will be listed higher.