access one computer from another

rssail81

My FIOS router comes in on the second floor and broadcasts a wireless network called BigWhale.  From that router I have an ethernet cable hard wired to another wireless router on the 1st floor called LittleFish.  Is it possible for me to access a computer on the LittleFish network from a computer on the BigWhale network?  If not, is there a better way to set up my routers so they are all on the same network?  How would I do this?