in total agreement with Tarmac .....best to purchase replacement bolts , gasket extra first..
if its from the ' y ' pipe back your looking to do then i'd suggest jacking the car from the rear to the highest advantage point you can safely do and put on axel stands. Once done the easiest way we have found is to run several 1/2 inch extension bars pushed together under the zed on to a correct sized socket on the nut at the rear of the 'y' pipe and use a breaker bar on the other end at the rear of the vehicle giving great leverage...........most come un done with the help of WD.Next is to lever the old system from the exhaust hangers....can be a pain but you' ll get there.
once its all removed its easy to refit the new one......if you need help or would like the zed shed to fit it let us know and will sort a time to get
you in
Buster