How to Delete a Comment I Put on Someone's Wall on Facebookby Daniel Hatter
You have full control over your name and content on Facebook, whether on your own Timeline, previously known as your "wall," or a friend's. This control includes the ability to edit and delete comments you write on your friends' Timelines. If, for example, you wrote a comment on a friend's post and now regret what you wrote or think you could have worded it better, edit the comment or delete it entirely.
Visit the Facebook website and log in to your Facebook account.
Type your friend's name in the "Search for People, Places and Things" box at the top and click his name when it appears below to go to his Timeline.
Scroll down your friend's Timeline to the post you commented on and move your mouse cursor over your comment. Click the pencil icon that appears on the right side of it.
Click the "Edit" button and make the desired edits to your comment. Press the "Enter" key on your keyboard to finalize your edits. Note that your edit history will still be viewable if someone clicks the "Edited" link below your comment.
Click the "Delete" button if you want to delete your comment completely. Click "Confirm" to finalize the comment deletion.