If you are unsure which Glock Gen you have, they are stamped into the front of the slide, as seen below. 

If you own a Gen 1-4, you will need to purchase the Gen 1-4 kit.

* GLOCK 42, 43, AND 44 OWNERS WILL NEED TO SELECT A GEN 5 KIT*

If you own a Glock Gen 5, you will need the Gen 5 spring kit.