Hi Lisa
You won’t lose anything if you first make a backup of your database and all your files. You can backup the database from within the manager ( Tools > Backup ) and will need FTP software to download all your MODx files and assets to your local machine.
The best thing to do is, if you haven’t already, set up a local development environment on your computer using MAMP (Mac) or WAMP (Windows). Then you can install Revolution and convert and test your site locally without touching the existing site.
As far as I know there isn’t yet a content migration tool to import content from Evo to Revo, so you’ll have to manually create all your pages again and copy and paste the content from your existing site. You could also try out
ImportX to import everything from a CSV file.
You might also refer to Bob Ray’s guide to
migrating from Evolution. It’s a little out of date but you should still find it useful.
Let us know if you get stuck!