Yes, what you can do is find out the default I.P of the wireless router and enter it into your browser (On a PC that is connected to your network) so it brings up the wireless routers page, and find out the default username/password and login to the router with those details.
On this page you should be able to find out your existing password. If that doesn't work, then you will have to set a new one, hopefully one you can remember. If you think you will have troubles remembering it, write it down on a piece of paper and leave it next to your router or save it in a notepad document.
