yes- you need the screwdriver looking tool to get the old staples out. Not sure what it's called but it's like a bent screwdriver with a 'v' shape cut out of it.
As for staple guns, I've got a few cheap and expensive ones, and TBH I always find the real cheap one the best- only I can never get replacement staples! The best one I ever had was from woolies about £2.99 it was fantastic.
I'm sure that ours just came from somewhere like B & Q. Very basic-works fine. I did our dining chairs-take off what is there -use it as a pattern-put back on. Do one at a time to see how it goes. Good luck.
So I'm going to have a bash at recovering a dining chair. Can anyone give me any pointers about buying a staple gun (particularly one I can buy online)? All other pointers gratefully received as I have never attempted anything like this at all but don't fancy shelling out for new chairs.