upgrade mx7 to cf9

Our company intranet site was built by a third party.  It's been using CF MX7 Standard.  They have an upgrade for the site which requires CF 8.01 or better.  I'd read of issue with 10 and thought it safest to upgrade to 9.  What's the procedure for upgrading?  I gather I need to purchase 11 with a downgrade to 9.  I understand there's a utility in the developer edition that analyzes the site for issues, which I'd like to use.  Thanks for any help.