Carry out the following steps:
Go to the dashboard and click on Pages and Themes.
Your new theme should appear at the end of the installed themes; click on Install, as shown in the following screenshot:
In the next screen, you'll see all the page templates you've created. Click on Return to Themes to get back to the previous screen.
You just installed your theme, but it isn't activated yet. Click on Preview if you want to look at it before activating it or just click on Activate to use it right away.