1stly do not try to clean up your disk manually.Your computer can compute which file is important and which is useless to run the system.
Disk clean up is always safe.
Sometimes deleting ''Temp'' named folders can cause you loss of important bookmarks,links,saved game,checkpoints,recovery files for unsaved text,xcel,power point or word documents,etc..Or make ur system slow fr sm moments.
So you must use ''Windows own disk clean up system''.
For that
-U go to ''Help'' if you are using any windows OS or vista.
-Then type Disk Clean Up in the help menu search bar.
-Then some advice or options will come with the underlined word ''Disk Clean up'' in Vista or Win7 or may be a ''go to disk clean up'' option in older Win OS.
-U click on that link .
That will take u to a new window.
U select your system drive ( in most cases its C drive )
-Then the system will find out tempoarary,unnecessary files and you will hav to select what types u dont want.You must select on ur need.You may select all.
-Then the system self cleans the disk by removing those unnecessary files.
Thats all.
Its most safest to use Windows' own Disk Clean Up system when you are working on your precious system.Using of external nonlincensed software may harm ur system..Its your choice.