It depends on the marker.
On the A5 and X7, it's a simple drop-in unit. You replace the existing mechanical gripframe with a new one, and BAM you have an electronic.
Any other marker with a non-removable gripframe, like the 98 Custom or some of the other ones, are a bit more difficult. For the 98C, you have to open up the halves and replace some of the stock components with the new ones. Read more about it here