How can I prevent Windows from prompting to restart my computer after an update?

"Launch regedit.exe
Navigate to HKEY_LOCAL_MACHINE\SOFTWARE/Policies\Microsoft\Windows\WindowsUpdate\AU.
Under the AU key create a new DWORD value called “NoAutoRebootWithLoggedOnUsers”.
Set newly created value to “1” to disable the automatic reboot."

"As an alternative to Kirill's solution, the Group Policy Editor can be used if it's available (it's not available in some editions of Windows):

1) Open the Group Policy Editor (Run > gpedit.msc)

2) Navigate to Computer Configuration > Administrative Templates > Windows Components -> Windows Update

3) Double click the No auto-restart with logged on users for scheduled automatic updates installations setting

4) Set it to Enabled

5) Click OK and then just close the Group Policy Editor

Illustration below:"