Low disk space on c

Hello,
Salaam.My problem is about low disk space on disk c.As a matter of fact when i open it there are very low memory occupying folders inside it but still it shows that there is only 35 mb free space.I have tried cleanup but still doesn't work.I have symantec 2008 and i can't update it because of this low space.I can't download any other antivirus because of this space problem.