In my experience, when wuauserv starts eating memory, the best thing to do is to wait until it finishes installing the updates and then reboot.
If you can’t or aren’t willing to reboot now, you can always reset wuauserv with the following BAT script (right click & run as administrator):
net stop wuauserv net stop bits rd /s /q %windir%\softwaredistribution net start bits net start wuauserv wuauclt.exe /detectnow
Hope it helps.