Did you Read The Friendly Manual? Most have a "specifications" section. If it just says "USB" not "USB 2.0" you have 1.x.
If you don't have a manual:
(a) Motherboard manufacturer website or system manufacturer website if dell, compaq, etc.
(b) Google Knows All
edit: or (c) try telling us what you have, AT foks know (almost) all too, or at least we think we do 🙂