It is buried away in the settings.

I have a different Sony TV to you so the following path may be slightly different on yours, but have a go.

Press theSettings button on the remote control (small cog or spanner)

From the onscreen menu click to the far left and click on Settings.

Click on Channels and Inputs and click on TV button shortcut.

Click to the right and select Digital TV.

The next page will ask to Select your default TV app for Digital.

The choices are Live TV and Catchup, (YouView) and TV (Freeview).

Select TV.

Come out of the Settings menus. Press the TV button on the remote control.

Now press the TV guide button on the remote control.

This should now have changed to the Sony TV guide which is Freeview.