How do I remove a tag from a photo or post I’m tagged in?

Hover over the story, click  and select Report/Remove Tag from the dropdown menu. You can then choose to remove the tag or ask the person who posted it to take it down.

You can also remove tags from multiple photos at once:

1. Go to your activity log
2. Click Photos in the left column
3. Select the photos you'd like to remove a tag from
4. Click Report/Remove Tags at the top of the page
5. Click Untag Photos to confirm

Soiurce :- https://www.facebook.com/help/www/140906109319589

Happy facebooking :-)