[PJ]

That can be tricky. Really depends how soiled it is, and if it's insulated on the inside and with what. Just pointing out the obvious, but can you just go at it with a couple toothbrushes, one with leather cleaner and the other with just soapy water, and give it a good wipe with a damp towel? Otherwise, depending on how much they're worth or how much you want to restore them, you can always take it to a professional garment cleaner as well. But depending on how much that costs, you might be better off buying a new pair if they're beyond repair.