Hi @charliediy,
The fact that they sound hollow is a good sign that if you're careful, you should be able to lift them without breaking them. Please exhibit as much caution as possible, as it is entirely possible you could break the tile.
Start by removing the grout around the relevant tiles using a Grout Removal Tool and a vacuum cleaner.
When the grout has been removed, you can use a pry bar with a narrow tip, such as this Craftright 380mm Wrecking Bar, to gently lift the tile. If the adhesive is already letting go, you may be able to do this without any other work. You can place something like a book on the adjacent tile to protect it and help with levering the tile off. Apply gentle pressure and work your way around the tile until it pops off.
If you gently try this without any luck, you could also try slipping some braided wire down through the grout lines so that you can hold each end of the wire on either side of the tile and use it like a saw to cut the tile adhesive away from the tile.
Once the tile is off, remove the tile adhesive from the back of the tile and the ground. You could try using a Paint Scraper for this. If this doesn't work so well, then an angle grinder with a flap disc will work. Just make sure you wear gloves, eye protection, a dust mask and hearing protection if you are grinding off the tile adhesive. Make sure you remove all the adhesive and give it a vacuum to remove any dust.
Once tidied up, you can use a premixed tile adhesive such as this Dunlop White Ready To Go Tile Adhesive And Grout to stick the tile back in place. Use a QEP 10mm Square Notch Plastic Adhesive Spreader to apply the tile adhesive to the ground and then apply a smooth coat to back butter the tile. When putting the tile in place, push down and move the tile side to side to break the ridges of adhesive and create suction between the two masses of tile adhesive. Check out How To Lay Floor Tiles for some guidance.
Allow the adhesive to dry for 24 hours before grouting. Check out How To Grout Wall Tiles as the process is much the same.
Let me know what you think and if you have further questions, please don't hesitate to ask.
Jacob
