There are commonly available drop-in LED upgrades for Maglite and Surefire P60-type lights. I've successfully Frankensteined one light with a soldering iron and a tremendous expenditure of profanity -- and it was an LED to begin with, making it much easier. Show me pics of your lights and I can render you my inexpert opinion.

In general you're best off selling, giving away or recycling your not-easily-upgradable incans and replacing them.