@Peruvian81 I would delete only enough to get nifi re-started.  Then I would want to go into the flow and look at what has caused it to fill up.   This is of course assuming you have enough space in the drive to begin with.

Next, I would recommend you should address nifi documented steps for disk configuration, and based on your flow, expand the content repository if necessary and if possible.    

Last thing to consider:  your flow may just need to terminate large flow files when they are completed at the end of the line.  If these are held in Q, and no longer needed, they are taking up valuable space.