Wordpress expert needed to install new theme

We are looking for a coder who is very familiar with wordpress to install a new theme onto our wordpress site. ? All data MUST be retained. ? Everything must be functional. ? The coder will install the site onto a local server first and will make the test site available for me to check out before uploading to the live site. ? We cannot afford to have any downtime on our site, so we are only looking for coders who have experience with this process. Thanks, Clay