U can delete everything...
And the remaining file that r in use cannot be deleted...
They are temporary dump of the present processes...
Dont try to delete file who get error when deleted...
Leave them and delete the others....
It would be better if u use a software named Tune Up Utilities...
It automatically deletes the unnecessary files...
There are many more softwares like these...
But be wise in choosing them..
If u find my advice good... please choose best answer...
Because this keeps us answering.... and encourages us...
to clear all ur doubts...
Anyhow... Cheers!!!