sessions in asp.net

Question

hi!
   i creating one seesion for storing filename. (fileupload control filename is stored in session) if i again select new file then in the session
old filename is gone and new filename is coming into the session. my aim is save the old filename. means when i click fileupload select filename old filename is saved in one session. and new filename is saved in another session. please tell me how can we do it.(how we take multiple sessions of fileupload filename)
(or) if any another process is there to do it, tell me the how can we solve. and give example code.
Thanks.