Hi,
Thank you for posting in Symantec community.
I would be glad to answer your query.
GUP machines can not be updated manually. GUP machines can only take updates from the Symantec Endpoint Protection Manager (SEPM).
Need to troubleshoot why GUP's are not updated. You can target those GUP's who are not updated from long time.
Refer these articles to start troubleshooting.
Test SEP to GUP and GUP to SEPM communication
http://www.symantec.com/docs/TECH153328
Troubleshoot client/server connectivity in Endpoint Protection
http://www.symantec.com/docs/TECH105894