What have you tried and what kind of problems did you run into? You do the xml sitemap submission from within your webmaster tools account - look under the "Site configuration" tab. The Change Frequency will be controlled by the software you use to generate your xml sitemap, not by Google.
Is there a particular problem you are having? You should only have to submit the sitemap once, ever. Google will automatically check the sitemap on a regular basis to check for new pages.
Change frequency should be set in the xml file and should really give an accurate estimate of how often the page actually changes. As said above you should be able to set change frequencies in the sitemap generator you're using and these should be accurate.
I generally keep my change frequencies to a max of monthly as I'm always updating even my most static sites. That said though it's not like google pays particular attention to the change frequency and will mostly crawl as normal.
Msg#: 4204186 posted 12:40 am on Sep 23, 2010 (gmt 0)
You can edit yourself. Or mass edit in a text editor tool (or for that matter in sitemappers like A1 Sitemap Generator). You can also leave it out entirely. If you have a specific page you want Google to crawl often, you could add change frequency just for that URL
There is no need to resubmit as others said. If your XML sitemap has been updated, you can also issue a sitemap ping. But absolutely under no circumstances remove/resubmit sitemap :)