If you have antivirus software installed, try disabling that before trying to install the Windows 10 April 2018 Update, as that may fix the problem.
You should then enable it and use it normally once the installation has completed.
You may even need to uninstall the software temporarily.
These should be safe to remove, but remember you can't retrieve them once they're gone. Click ‘OK’ then ‘Delete files’ to remove the files.
If you want to create more space, click ‘Clean up system files’.