Hello,
I do have a good bit of experience with Wordpress, upgrading, etc, and I can have your project completed within 5-7 business days. Here's how I would go about this.
Step 1:
Duplicate the site onto a subdomain/domain, including existing content, themes, images, etc. This would best be done on my server, just so that I can duplicate everything perfectly.
Step 2:
Apply the updates necessary (WP, plugins, themes, etc)
Step 3:
Assist you with changing the theme as you like. While I'm no graphics genius, I can help you get this put together well enough.
Step 4:
Upon approval, do one final export of posts from old domain to new, adjust site domain in new wp install (to reflect current domain)
Step 5:
Import from new to old, AFTER backing up the old first.
If you'll look at my profile (click the link directly, don't go by what they show in this specific bid), you'll see 100% project completion, 100% positive (5 star) feedback, and a link to my own site where I've done the same for better than 10 years now. Your project will be completed with the same diligence and persistance. Your task will be completed within a 2-3 day period of time, and be given everything needed to be done right.
I look forward to hearing from you and working with you on this project.
Tom Whiting