In Task Manager/Processes click on Memory and that will sort to the highest users.
Right click on the highest service host then select Go to services and whichever is the bottom one is the service that is hogging the memory.
To see what each service host is covering, download Process Explorer then hover over each service host where you'll get a pop up listing those services.
https://technet.microsoft.com/en-us/sysinternals/processexplorer.aspxI don't know if you still have to do this with Process Explorer or if the latest version already incorporates these, but click on Options and ensure Verify Signature is checked then hover over VirusTotal.com and check its box.
You'll then get a VirusTotal column where they should be all blue but if you have any red highish values divided by 50ish then those should be treated as suspect.
The Windows Update service hogging CPU and memory in Win 7/8 is no longer a problem since MS has updated the Windows Update Agent each month for the next month's updates - but should you not have it then you can manually download from
https://support.microsoft.com/en-gb/kb/949104