If you want to install the full version and already installed the trial version, you normally do not need to uninstall the trial version. The trial version will be overwritten when installing the full version - provided that you install the full version to the same location as the trial version and under Windows choose the same application(s) in Plugin Installer. If you are not sure, you can nevertheless uninstall the trial version before installing the full version.
To uninstall MetaRaw under Windows go to Start > Control Panel > Uninstall a program (Windows 7) or right click the Start button, select Control Panel and click on "Programs and Features" (Windows 8 & 10). On the appearing dialog double click the appropriate item to uninstall it. Under MacOS X you have to manually delete the "MetaRaw.plugin" file or the MetaRaw folder from the Plug-Ins folder of Photoshop or Photoshop Elements. Alternatively you can use the Uninstall icon of the .dmg file to remove all copies of MetaRaw.
Installation under MacOS X
Double click the downloaded .dmg file and then drag and drop MetaRaw.plugin file or the MetaRaw folder onto the one of the icons on the right in the same window. For example if you are using Photoshop CS6, please drag and drop the MetaRaw onto the "Photoshop CS6" icon. If Photoshop should be running, quit and start it again in order to use MetaRaw. Alternatively double click the Install icon to install MetaRaw into all available Photoshop and Photoshop Elements versions.
Installation under Windows
Double click the downloaded .exe file and follow the installation instructions. When Plugin Installer shows up, activate the check boxes of your preferred application(s) and press the Install button.
You can run Plugin Installer at any time from Start > All Programs > The Plugin Site > MetaRaw > Plugin Installer. Then you have more options than during installation, e.g. an Uninstall button.
If you install a new version of Photoshop Elements and MetaRaw is already installed, you do not need to run the full MetaRaw installation again. You can run Plugin Installer from the Start menu and use it to install MetaRaw into the newly installed version of Photoshop Elements.