You have to go into your routers internal settings and then to the security tab where you will see the router password and there you can change it. If you do change it make sure you save and exit and write it down and keep it in a place where it won't get lost.
The routers owners manual should have instructionas on how to get into the router and if not then you look on the bottom or side of the router and you will see a default address something like 192.168.1.1 which can be differnt on various routers and you take that and tye it into your browsers address bar and hit enter then a user name and password box will come uo where you fill it out and hit enter your then in the routers internal settings.
To make a security code you need to enter the routers address into the address bar on your browser. Chances are that it's 192.168.1.1 but you can find it easily by looking on the bottom or side of the router, the users manual or the web page of the brand of router that you have.
Once you enter that address you will get the routers log in window where you will put the user name and password of the router. That information can also be found on the web page or in the user manual of the router.
Once in the routers internal settings go to the wireless page and select the wireless security sub menu and that's where you can make a security key using one of the routers key generators (WEP , WPA or WPA2) , WPA2 would give you the best security key strength , also this is where you can view the security key once it's made.
Write down the security key and save it in a safe place for when you may need it.
Save your changes and exit the routers settings.
If you need the password for your network then on any computer that is currently on the network go into the ciontrol panel and select Network and Internet , then select HomeGroup , then select view and print the homegroup password and the next page will have your homegroup password.