I want to change my site from a .co.uk to a .com. I have indexed pages on the .co.uk. I've deleted the sitemap from webmaster tools, and uploaded new one to the .com. Anything else I can do, apart from backlinks, to get the .com indexed faster and replacing the .co.uk pages?
301 all co.uk pages to relevant .com pages so that link value should pass to your new pages from old pages.
One more thing you should do. There is an option 'change of address' in Google webmaster tool. If you want to migrate your website to some other domain, you should mention that domain name there.
how old is your website? because if it 2 to 3 years old and is good optimized with Google then do as manish.chauhan has told. i think Google will index your website right away if the reputation of your website is good.