I assume you've either got silver grey or anthracite 'synthetic suede' then.
But I think your parcel shelf cover may just be cloth?
The seats can be cleaned with a mild soapy water solution for the cheapest method, or you can pay a couple of quid for some autoglym, car plan upholstery cleaner (specifically NOT leather cleaner).
I was quite hard on my 'synthetic suede' with a a good nail brush and it didn't seem to do any harm in over 100,000 miles - the cloth part I was a bit more gently with, but that was just a softer brush to work the soap/cleaner in and then a damp cloth to wipe it off, and finally plenty of terry towels to dry it up.
The parcel shelf is a bit of a bugger as an dampness will make the glue unstick and you and up with baggy cloth on the parcel shelf, so you'll need to use a wet wipe or something similar and take it bit by bit.