The previous version of MX CSS Menus was MX CSS Dynamic Menus. "Version" is a lot said though, cause you can actually see these two Dreamweaver extensions as two different products given all the changes and improvements in MX CSS Menus.
Note: After the MX CSS Menus release, MX CSS Dynamic Menus cannot be purchased anymore. Support will continue to be offered for the clients who have the old version of the product.
Say you already own the first version of the product, MX CSS Dynamic Menus, and you want to purchase the new version, MX CSS Menus. If you have websites in which you generated CSS menus with the first product version, and you now want to benefit from all the new features MX CSS Menus brings, you will simply have to remove the old CSS menu and apply a new one.
Note: It is recommended that you do not uninstall MX CSS Dynamic Menus, at least until you "upgrade" all your sites CSS menus, so that the old server behaviors would still be recognized in page.
If you had generated a static menu (non database-driven menu) in your site with MX CSS Dynamic Menus, and you want to replace it with a new CSS menu generated with MX CSS Menus, delete the corresponding server behavior (select it in the Server Behaviors tab of the Application panel and click the Minus (-) button above the server behaviors list) and apply the CSS Menu Wizard - you will have to manually enter the menu items again.
If you had generated a dynamic menu (database-driven menu) in your site with MX CSS Dynamic Menus, and you want to replace it with a new CSS menu generated with MX CSS Menus, delete the corresponding server behavior. The used recordset will remain in page. Apply the new Database-driven CSS Menu server behavior using the respective recordset in page, and a menu identical with the deleted one (regarding the menu items) will be generated in page.
After applying a wizard or server behavior from MX CSS Menus, you will notice in the includes folder from your site a new directory named cssmenus2. No file from the old folder cssmenus was overwritten. However, even if the old .css file was not deleted, it cannot be used with the new CSS menu - the .css files (92!) in MX CSS Menus were rewritten from scratch so that skins could be easily customizable, therefore the structures of the old and new .css files are totally different.