Read the manual, page 22 says to use a 3/32" punch to drift the roll pin out the bottom of the grip. Use care to not damage the insert as the pin is in there tight. I found the medium insert that is already installed to be the most comfortable, but you should still try all three to se what works best for you.
"THE CONSTITUTION ONLY GIVES PEOPLE THE RIGHT TO PURSUE HAPPINESS, YOU HAVE TO CATCH IT YOURSELF." ~BENJAMIN FRANKLIN.