Cleaning very grubby cream chair covers

[ineedsomepeaceandquiet]

I need to clean my cream dining chair covers (a pre child purchase) but they don't come off. I have tried vanish which didn't work. Would be grateful for any other ideas.

I used rug doctor spray stain remover, a damp microfibre cloth and a bit of elbow grease and my chairs look much better (not totally clean but a hundred times better than they used to be)

p.s. I got the spray from the supermarket where you can hire rug doctor carpet cleaning machines - the spray is on the stand with the machines and not on the shelf with the other cleaning products.