To prevent problems with other wifi networks you should use the 5 GHz network if your wifi router and all connected devices support this. Check the technical specifications of your devices to find out if they are supporting this frequency/standard.
In order to configure the 5 GHz wifi you need to open the router's configuration website. The address is printed on the back of router or can be found in the manual. The configuration website likely has one of the following addresses:
Use the login data printed on the back of the wifi router for access to the configuration website, if you have not already changed the login credentials.
Depending on router type and software version, the configuration interface and setup differ. For the corresponding instructions, please use the router's layout and menu bar as a guide: