Pretty easy to remove the cylinder, although if you're not confident or unsure about it, get a gunsmith to do it for you.

It all unscrews (spanner at the filler valve end) and then you can unscrew the action from the cylinder at the breech end. Obviously, commons sense applies here You're working with parts of a compressed air system no oil, no dust/grit/dirt anywhere near the ****ing thing while its in bits.,

I converted my S400K to a S400 Classic - and recently had the barrel and tube reblued - the quality of the original blueing was frankly terrible. You pay extra for a British made gun and you get screwed by crappy blueing