Here's how to remove various items. If you're having trouble with a bad startup, particularly after a crash, you can try removing the preferences first, before reinstalling.
Uninstalling the SynthEyes Program
Windows: Use the standard Windows Add/Remove Programs control panel.
macOS: Delete the folder /Applications/SynthEyes
Linux: Delete the folder /opt/SynthEyes
Uninstalling the License Data
Here are the directions for removing the license information from a computer. Obviously, this is different than removing the program itself!
Windows: Open the start menu's search box, enter regedt32.exe, then start it. Expose successive items to reach the key HKEY_LOCAL_MACHINE/SOFTWARE/SynthEyes and delete it (includes all the values in it).
macOS: Delete the folder /Users/your name/Library/Application Support/SynthEyes and also the file /Applications/SynthEyes/registry if it is present. (You need to opt-click Go in the Finder to reach the Library in your Users folder.)
Linux: Delete the folder .SynthEyes in your home directory (ie ~/.SynthEyes) and also /opt/SynthEyes/registry if it is present.