You can do it yourself, or have it proffesionally done.
If you do it yourself, buy a 3.5# connector, glockmeister competition trigger spring, reduced power striker spring, and polish the trigger bar, bottom of striker, and the connector. that'll give you a 2.5-3# trigger.
For the very best possible glock trigger get it done by charlie vanek. He's got the absolute best glock trigger. He does a secret modification, and the trigger breaks at 1.25#'s. The weight is just gravey, the trigger is shorter, resets faster, and breaks sooo smooth. I got one on my Glock 35 that I use for IPSC competition. CGR and om Novak do pretty good trigger jobs too, but Charlie has the hottest thing out there. Do a search on Glocktalk or Brian Enos and read all the rave reviews from real competitors.