Hi guys Would just add that if using an angle grinder to remove grout, you need to be megga careful of the tiles - a fraction off line and you will be cutting into your tiles before you can correct the grinder. The other problem is that as the discs are circular, you can't get into corners or right to the top and bottom of tiles.
In my opinion, a multi tool fitted with a diamond blade is a better option. This is less likely to damage any tiles, removes the grout really easily without filling the room with dust and due to the shape of the blade, gets into difficult areas.
These multi tools can be hired, including blades, if you don't own one / can't borrow one.