First, you need to log into your router. To do that open your web browser and enter in 192.168.1.1 or 192.168.0.1 and press enter. If that does not work, check your routers manual.
If you forgot your routers username or password, you will need to reset your router. There will be a button or a small hole called reset. You need to hold that down for about 5 to 10 seconds. This usually resets your router back to its default settings. Please check manual or vendor website for exact steps.
Once logged in, look for wireless security or wireless settings. In there you want to set the security to WPA2-PSK. For encryption select AES+TKIP.
For your SSID, select something you will remember and that identifies your wireless router. Do not use any passwords here or any detailed info about yourself or your address.
For your wifi password, (WPA-PSK) enter in a difficult and long password. It would be something you can remember, but if you forget it, you can always log back into your router and change it.