My router keeps dropping the internet connection. The ISP checked and said it was "unstable". They sent me a test modem which I am using now and this solved the connection problem. They suggested I needed to speak to Belkin to upgragde the software? How do I do this? Also I just noticed a 'reset' button when I took it off the wall to check the model no. Should I press this at any point?

The reset button resets the router to its factory default settings. It's really there for if you forget the password into the router you can reset it and set it up from scratch again. Beware of this button because you will have to set the router up again if you press it - including your broadband username and password which most people have long forgotten and lost the documentation for!

As to the connection being dropped, this reeks of MTU problems - ask your ISP for their reccomended MTU setting and then put that in the router, if thats already in then try both a lower number then a higher number and see what happens.
(MTU is Maximum Transmittable Unit - essentially how big the packets it can transmit back and forth - if the packets are bigger than the router will accept then they get dropped, and if they are smaller then you are losing speed) - dropped packets = dropped connection.

And finally, upgrading the router software. Go to Belkin site and find the firmware for your router model. follow the steps to install this on the router.
In fact I've just found it for you and linked it below, hope it helps
http://en-uk-support.belkin.com/app/product/detail/p/4784

Word of warning - follow the steps exactly when updating firmware - you can easily 'brick' your router if anything fails or you cancel halfway through.