How do I connect my PC to the Wireless 5GHz-High band?

As mentioned you normally should connect to the 5Ghz band but I have occaisionally seen my desktop connect to 2.4Ghz even though 5Ghz is available. You should be able to disable 2.4Ghz in device manager if you ONLY want 5Ghz. To do this go to Device Manger>Network Adapters and find your Wi-Fi adapter. Right click on it and select Properties>Advanced and hopefully you will see something like this:

If you set 2.4 Wireless Mode to Disabled that band will not be used by your wi-fi adapter.