How do I know if I have the latest firmware version installed?

Hi,

I did

ls /lib/firmware/iwlwifi-3945*
/lib/firmware/iwlwifi-3945-2.ucode

but my wifi card  very rarelly, sometimes disconnects (router is ok)

I see there are 5 versions for this firmware on the site.

how can i check if I have the latest? I'm running Ubuntu 14.04 and

uname -r
3.13.0-37-generic

Thank you!

Luis Louro