Cannot get water to switch from tub to showerhead?

I have a tub/shower combo which has the little "pull-up" valve that switches the water flow from the tub faucets to the showerhead. I have had increasing problems having to jiggle the little pull-up on the faucet to get it to switch and now it simply will not do it. Is there a simple way for me to fix it without payng huge plumber prices?

Answers:
You will need to replace the tub spout. The link below explains it.
If it doesn't have a allen screw, it will screw off a piece a pipe.
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