Yeah, take off all of the grip tape, even the factory applied grip. Then once you're down to the bones of the racket, you can apply any kinda strechy grip tape over the handle as tightly as possible. That should make it a bit smaller.
Thanks for the reply Jan. I am actually wanting to shave the grip down a few sizes so a replacement grip can be re-applied so I don't loose that nice cushion feel. Haven't done it before so I wasn't sure if anyone had any special technique to keep the grip as smooth as possible.
I have a couple of questions....
Are you resizing a handle for yourself....???
What size is the handle now...???
4 3/8, 4 1/2 etc. ???
I guess a more important question is what size is your hand in relation to the handle...???
In general you always want the largest handle that you can hold on to with a loose and relaxed grip. When your handle is to small it requires you to tighten your grip and use the forearm muscles to help control the racket head. In general this is counter productive to playing your best tennis. I apologize for my lengthy reply. But if you are modifying your own handle size I urge caution. If you are modifying the handle for someone else then please feel free to contact me as I do have some techniques to help.
Recently I tried a new grip made by Babolat called Skin Feel. It's thin, and in my opinion reduces your grip size by 1. I used to play with 4 1/2, but tried 4 3/8. I found that I liked it better, as it gives me a more whippy feel to my swing. With the addition of the aforementioned grip, I can use my old racquet again! You can try to shave down the handle, but my stringer said it might weaken the grip (foam-like material on some racquets) if you shave too much. By not using a replacement grip at all and merely using an overgrip, you can reduce the size by 3 points! Unfortunately, the handle becomes too hard for me and can be painful on harder swings, and you can feel the butt cap (I grip my racquet very low on the handle).
While increasing the size is easy, you're pretty limited when it comes to decreasing the size of a grip, more specific the racquet handle. These days, most handles are made with injected foam I assume could be shaved. You would want to pay attention not rounding the 8 bevels. I don't know if you could use a file, block plane or a sander because you may lose the integrity of the foam becoming brittle. Removing the grip and using an thin overwrap may work, but you will lose the comfort and cushion you are looking for. Try finding a thinner grip replacement and wrap it very tightly around the handle. You can also use a wood dowel or rolling pin to flatten the grip once its on the handle. Last resort, sell your racquets and pick up some new ones with the right grip size.