You would need to delete the license key and restart the computer/laptop:
1) Right-mouse click the Primus Softphone program in the Windows tray and close the program so that it's not just minimized
2) Enable hidden folders in Windows
3) Navigate to C:\ProgramData\Primus\Primus Softphone4) Delete the folder named "5.0"
To enable Hidden folder:
Open File Explorer from the taskbar. Select View > Options > Change folder and search options. Select the View tab and, in Advanced settings, select Show hidden files, folders, and drives and apply at bottom.