What is the issue is un-instaling it...I hope you have admin rights on the PC.
There are many ways to un-install. Try following the below steps:
· Go to Add/Remove Programs and remove the program
· Reboot
· Try install
· If that fails, follow the manual removal process.
· Try the install again
· If that fails, run the cleanwipe utility. As a precaution, have a backup of the OS before using utility (This utility is provided by Symantec Technical Support)
· Search for and remove any old Symantec Endpoint Protection .MSI files.
· Install new version
Since I dont completely understand your issue in uninstalling, you can check these links in case of any issue. Do let us know, if you have any further query.
How to uninstall Symantec Antivirus, Symantec Endpoint Protection,and Symantec Endpoint Protection Manager, and what to do if that fails
http://www.symantec.com/docs/TECH104790
Manually Uninstalling Symantec Anti-Virus or Endpoint Protection
http://www.symantec.com/docs/TECH164769