My lower lip sticks out a bit more than my upper lip. (Photo)

Hi there,
Unfortunately there is no way to reduce lip size without a surgical reduction. You could possibly consider a temporary filler for the top lip so the lips look similar in size. 
If you are considering a lip reduction it is a common procedure and can be reduced in an office setting.  It is done usually under local anesthesia and patients are made quite comfortable.  The sutures are placed on the inside portion of the lip to help conceal a scar.  Final results are between 3-6 months. I hope this helps.
Best,
Anil Shah MD

It is considered normal that lower lip is slightly (up to 30%) larger then upper lip. In-person evaluation is needed to give you more info. Lip reduction is very easy, simple surgery with predictable result. Good luck.

Andrew.   Frontal view photo would help, but your lower lip does not look overly large because the lower lip normally is a bit larger than the upper lip.  Be sure to consult with a board certified plastic surgeon to further investigate options.  Good luck!