Please help, how to delete of my computar but not my book?

Hi this is probebly a question with a really obvious answer but how do i delete something off my computar with out the My book essential automatically deleting it to.  I tried with some photos then went into the system and pressed refresh back up, or something and both had gone down in size…slightly worried about this because i want to free up lots of space on my computar but if  i cant then its a problem!! please help thanks :smiley: x