my stock 370 heatsink wont fit due to capacitor in the way
what can i do?

You sure you're using the correct heatsink/motherboard?

yes im 100% sure
it was from a brand new 370 upgrade and i have to use my old socket 370 heatsink cos this heatsink fits bu cant due to a capacitor in the way--the cpu works fine

Sounds like you might have wanted to read up on issues with the motherboard that you have. This is an all-too-often occurance with home-built machines. Unfortunately, motherboard manufacturers don't always follow all the rules on capacitor placement. The best way to avoid this problem is to do research on the board and heatsink combination that you want to use to ensure that no one has had issues like the one you speak of.

what if i were to extend it or take the capacitor off

If you took the capacitor off, your motherboard wouldn't work.

Is it the heatsink clip that is interfering? If so, I have seen some people do some fancy bending of the clip in order to "fix" the problem. This creates other problems though. It would be safer to buy a compatible heatsink rather than resort to modifying the heatsink.