Are you sure you have the google-experience launcher? The one that comeswith the Nexus 5 and has integrated Google Now on the leftmost screen? It does not come with the Nexus 7 update, it is Nexus 5 exclusive. You CAN sideload it, but since you mention "Five Homescreens" you don't have it. You have the stock launcher.
If you are using the Nexus 7 'stock' launcher you cannot remove or add homescreens. You could install Nova Launcher or another third party launcher. You can easily add and remove screens on these, through pinch out and drag screen to the 'trash can' or 'X' icon.
Specific to G.E.L:
You simply remove all the shortcuts from the rightmost screen and it will automatically remove the screen itself. The reverse is true also, drag an icon out of the app drawer over the edge of the rightmost screen and a new one will be created.
Side Loading GEL:
Phandroid 'How to' With links to the apk files
You can easily sideload GEL and you will only have one homescreen by default, and integrated Google Now. This should work on any Android 4.0+ Device. I have tested on 4.2.2 and 4.3 and 4.4 on Galaxy S4, Nexus 4 and HTC One.