Hi, I have done this on a couple of Tiger 1s,
First thing to do is cover the area around the hatches with DUCT/DUCK TAPE NOT masking tape, This will protect the surface so you will not need filler when you have finished,
To remove the hatches I use a STEP DRILL very carefully, they come in different sizes ,
DO not push the step drill too hard otherwise you will melt the plastic and do not go in to the plastic too far you need to leave a lip for the replacement hatch to rest on, which means finishing with a small file and an abrasive board.
I would avoid the MATO metal hatches and instead use the TAIGEN hatches they are much easier to fit and look a lot better and have less parts ,
If you have not done so I would recommend you take off the Turret before you start on the hatches.
Shaun.