transit 1998 sluggish?

I`ve identfied what the problem is,I`ve tried to fix it but need to know I`m going about it the right way.
Apparentely it`s the bush in the air flow control, I know where it is and have stripped to that point.
How do you pull the bush,I`ve undone the 3 allen screws and removed the piston,I just can`t pull the bush out,I don`t want to miss something and knacker it.