Endpoint Protection

I have lot of remote sites and link is 1 Mbps. can i upgrade my SEP from 12.1 to 14 through GUP

No. GUPs only provide content, they do not provide the option/ability to do client upgrades.

I dont have any SCCM or desktop manager to push client on remote site and through SEPM the link is small

Is there any way to use GUP for SEP upgrade?

No, GUPs do not support upgrading clients. They only provide content to clients.

For slow links, you can copy a package out to that location and use the push deployment wizard, which is a standalone app, see here:

http://www.symantec.com/docs/TECH195705

you can use Auto upgrade, it will send only the differntial package from the currect version and the latest version you are trying to deploy. usual they are multifolds smaller than the regular client push. these articles applies to both SEP 12.1 and SEP 14 though the title says 12.1

Upgrade Endpoint Protection 12.1 clients using AutoUpgrade

Upgrading client software with AutoUpgrade