Lol. You've been on here 5 years and don't know what a remap is? CS has failed you!
Basically, they plug your ECU into a computer and change the way it controls things a little bit.
There is a risk, but as long as you go to a trusted, experienced mapper, it's very very low indeed.
A remap is not free, it takes a fair bit of time to get it right and the necessary equipment is very expensive.
You can get 'off the shelf maps' with something like the RS tuner (allows you to remap your own car) or you can get a proper custom map done; this will give you a better result 99% of the time.