I want to put meprolites on my CZ75.    How hard is this to do?

Like everything else it is hard the first time and easy the second time. I just did one of mine a couple of weeks ago.
Front sight: Drive out the pin that holds in the sight with a punch. Use a mallet and a block of wood and drive the old sight out forward. If you look underneath the sight you will see a slot cut in the bottom. This is what the retaining pin goes through. You will have to duplicate that cut on the new sight. That is the hard part. Some people put the sight in and drill the hole with the sight on the slide but it is very easy to botch up the slide that way. The slot has to be perfect and the hole large enough or you won't  be able to get the retaining pin back in.
Rear sight: I use a sight pusher. Banging on a tritium sight with a hammer and a punch is a good way to ruin it.
All four of my CZ's have Meprolight sights.
Allow yourself plenty of time when you start this project.