How do you re-tile the bathroom wall above the bathtub?

Tear out old walls and replace with concrete board, go all the way to ceiling for a finished look. Fill in screw holes and seams with mortar not drywall mud. Thin set your new tile. Will last another 50 years or more. Make sure you have a good tub, like cast iron enamel, that will also last. Now would be a good time to replace if need be. To replace a tub, you have to tear out the walls

Tie a good tile around them, the to a trucks trailer hitch and pull them out slowly

If they are loosening and coming off moisture has more likely got behind them. More likely moisture resistant drywall that doesn't really last. Best move would be to remove down to the studs, add insulation if needed, put up cement board, and retile.