Advice needed on NZ setup

We have recently moved to NZ from SA and staying at a rented house. We have a Slingshot uncapped broadband connection with a NetComm N300 wireless router in the central lounge area. Now while this is fine for laptops & tablets in the immediate area, it is not so good for connection to far away bedroom and study PC's. We tried our Netgear dongles from SA but only got about one bar signal strength... insufficient. The furtherest point required is about 20 meters through about 5 wooden walls.

Please could anyone possible offer advice on above scenario, much appreciated.

Thanks in advance

Videoman

Can you remove the antennas?

If so, your cheapest option is to purchase a couple of Rubber Duck antennas that will give you a bit of gain.