I would like to upgrade to the newest Parallels Desktop version.
Is there a chance I lose some data in Windows after the upgrade?
Do I have to uninstall the current version first, then upgrade?
By upgrading/updating Parallels Desktop nothing in Windows virtual machine will be affected at all. All applications and data will stay in the same condition and place you left it before upgrading.
There is no need to uninstall the current version of Parallels Desktop before upgrading, just launch the installer of the newer version. It will completely replace the existing one.
When the upgrade is complete, start your Windows virtual machine, then wait for Parallels Tools to update and restart Windows.
If you would like to transfer the existing Windows virtual machine to another Mac, please see KB 114118.
If you wish to downgrade to Parallels Desktop version you had before, just download and launch the installer of the older version. It will completely replace the existing one.
Parallels Desktop 12: Download
Parallels Desktop 11: Download
You can find the outdated legacy Parallels Desktop versions in KB 5802.