Even during times of terabyte(s) sized hard drives you can come across situations when C: drive if full and you have to free-up some space no matter what. Besides obvious solutions such as deleting large files from desktop and so on, you can try following:

Warning: Some of these tips are not for beginners and make sure you know what you are doing.

• Uninstall unnecessary programs
• Delete temporary files. This can be done:
  • Manually
  • Using built-in Windows Disk Cleanup utility
  • Using third party software such as CCleaner
• Move Page File to another disk
• Disable Hibernating
• Disable System Restore and Previous Version
• Disable Shadow Copies (servers)
• Check size of Windows Search Index file at C:\ProgramData\Microsoft\Search\Data\Applications\Windows\Windows.edb
  Rebuild search index if it’s too large: Control Panel > Indexing Options > Advanced > Rebuild
• Delete server pack and updates uninstall folders. These are hidden system folders such as:
  C:\WINDOWS\$NtServicePackUninstall$
  C:\WINDOWS\$NtUninstallKB2653956$
• Not recommended but you can temporarily move C:\WINDOWS\ServicePackFiles to another location.
  In this case you may want to update path values in registry in following location:
  HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Setup