Hi,
Please, run the Disk Cleanup wizard built-in in your O.S. to... cleanup your disk. If it is not enough, you may call to Tech Support to get the CleanWipe tool or the manual uninstallation procedure.
To install SEP to a custom path, no need for tricks, just go thru the product documentation to customize your SEP client installation package and then export it. Please, note that some shared components will be still installed on C: under paths like "programdata", "common files", "symantec shared", etc. If you have issues with those folders, you may consider that you are simply not meeting our system requirements and you need a bigger C: drive. Taking in consideration that SEP is using only few hundreds of MBs, I don't believe that moving the SEP from a partition to another is enough to obtain a reliable server i.e. not always at risk of running out of space for other reasons like just some Windows patches.