Hi Graeme
I'll take a stab at helping you even though Geoff could probably do it better.
Start by minimising all all your open screens either using the minus button or the square button in the top right hand side of the screens till you reach your back ground screen.
Then click the right hand mouse button either once or twice and you will bring up a box at the bottom of which is the word properties click on the word properties.
This should bring up a box with the heading display properties under which is a header saying SETTINGS click on this to open it.
On the bottom left should be screen resolution and it should be probably at a minimum of 800 by 600 but higher is ok too i run my computer at 1024 by 768
Also Graeme if you want to view high resolution photos that are large then you can up your screen resolution to see more of the photo's in the screen
Hope that this is clear and precise and helps mate
Regards Mark