My left testis is bigger in size than right testis why and what i can do to decrease its size?

Normal man: Of course it is. That is how it is for a man. One testicle is the dominant one and the other is there for back up. This is normal.

Probably okay...: Oftentimes, an enlarged scrotum (on one side) is mistakenly perceived as a large testis by many laypersons; in fact, it's hydrocele, which is more common in the old, and if so, surgery (hydrocelectomy) can successfully get rid of it. So, it's worthwhile to see a urologist for detail.