Do I need to uninstall the old version before installing the new one?

You do not need to uninstall the old version unless required by the installer of the new version. You can simply install the new version and it will inherit the software license and configuration. If you uninstall the old version, the software license and configuration will be cleared. For more information, please refer to Install, Update & Upgrade Primo Ramdisk. 
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What is Maximum RAM Usage?
Why can't I successfully put the page file on the virtual disk?