Launch TEST4U with administrator privileges and try to upgrade again.
If this fails then run TEST4U having the keys ctrl+shift pressed.
This will clear TEST4U's cache.
When the clean up is complete you will be asked to start TEST4U again.
Try the update process again.
If you still cannot complete the update then uninstall TEST4U and download the latest full version of TEST4U from :
https://www.test4u.eu/en/mod_downloads/files
Install TEST4U again.