If the MATLAB uninstaller was unable to complete, try executing the uninstall.exe from $MATLAB\uninstall (where $MATLAB is the folder where MATLAB is installed). For example:
If you are unable to complete the uninstaller, you can manually delete the MATLAB installation folder.
Afterwards, you can remove the MATLAB entries from the Windows System Path. For help modifying the Path in Windows, see the related article:
How do I set my system path under Windows