Open task manager (ctrl/alt/del) & see if there's a LW process running. If there is, end the process. Now try to install the new version.

If you've tried to uninstall LW thru add/remove programs, this can cause problems. You might have to use your computer's search to look for LW files/folders & delete that way.
The correct way to uninstall LW is via start > all programs > LW & use the uninstall option there.

Normally, installing a new version will automatically uninstall the old one. That's why I wondered if you'd tried to uninstall thru add/remove programs & run into trouble because of that.