Unbolt the downpipe and crossover. Soak the bolts good the day before with something able to penetrate. Make sure you have two new donut gaskets for reassembly.
The rear CAN be removed from the top on the S1, but your airbox will have to be out of the way. It'* tricky to get it in and out.
You need to have a swivel-head torque wrench for reassembly, and a deep-well 14mm and 15mm socket to clear the studs. You'll also want gaskets for the manifolds now. OEM had none, but after removal, you're better off putting them in. They're cheap and readily available locally.