tryed 6 anda bit size dont fit and 7 wont hammer in is it possible to cut them off?
 
probably but personally i prefer to weld a nut or similar to it rather then cut away

heat helps release em a bit too
 
probably but personally i prefer to weld a nut or similar to it rather then cut away i dont get what u mean sorry.

what could i use to heat it up. because isnt it flamable
 
as the bolt is rounded out you have a few choices

1 - drill/grind/cut the head away to release which can be awkward with access to get in there

2 - weld a nut to the top of the old one and use that to undo it

in the process of welding the metal will get heated up and expand then contract as it cools, bolts usually being smaller will cool sooner slightly and will help loosen off the grip