I'm assuming this means that you've lost the password for your wifi connection with your home router. What you probably will want to do is log into the router itself and change that password. If this isn't the situation, you probably don't want to be fiddling with router settings as I suggest below.
This is not a first resort, but it is what I would do (maybe other people have ideas for finding the password to a router to which you are already connected?)
First (assuming that the original username/password remains on your router),you will want to look up what that username/password will be. Often searching for the make/model of the router with something about "default password" in Google will yield this information. Sometimes it is 'admin' and 'admin' or something like that. Once that's established, you can connect your laptop physically (with an ethernet cable). You can type in the router address (probably 192.168.0.1 or 192.168.1.1) into the web browser, where it should ask for this username and password set.
From there, depending on the router (manuals often available online), you can go into wireless settings (probably under a security tab) and change the password to something that you remember or write down. This will mean that you will have to reenter this password on your laptop when you connect wirelessly as it will have changed. I like to write the password (and username/password for the router itself) on a post-it note and attach it to the router itself, in case I forget.
You probably wouldn't need to actually physically connect the laptop, but it can keep you from accidentally password-ing yourself out of the wireless network.