Title says it all really! 
Since PFB came along I have been religiously backing up my photos to my laptop. I realised recently that it was running low on space (less than 10% free and bar was red- dell Inspiron).
I deleted a lot of stuff off, haven't added any new photos since and it's back to critical again.
How can I work out what is using up my memory/what is safe to delete?
Thanks