how do i change the size of my screen?

I'm running XP. I thought I had made it plain but what happens is that the picture which used to end at the edge of the screen now extends past the edge so that in effect I am only seeing the middle of the picture. To see the right hand side for example I have to click the arrow on the bottom to swing the picture over but then I cannot see the left hand side so I have to click the left hand arrow to swing it back again. I HAVE been able to reduce the size of the picture but then I'm seeing even less of the full screen and have to swing it even more to see the sides. Its impossible if I do internet banking because the "proceed" button is always right on the edge of the picture. I will have a look at what you have all said and try to adjust the size.

thanks

Dave

I've read what you have all said. If I right click and get "properties" up-all I then get is a small window saying I am on yahoo answers but no chance to change anything. If I go to control panel theres nothing there about personalise. I really don't know what to do. I tried reducing the pixels which did reduce the size of the picture but in fact what it did was give me an even smaller slice of pie. I give up-there must be a way to do it but I don't seem to be able to find it. If any of you know please give me some more information

thanks

Dave

Well I have finally done it. At the right hand side of my screen at the bottom is a magnifying glass with a percentage number alongside it. Having had the computor for about six years I have not noticed it before!!!!!!!!!!!!!!!!!! Well it was showing 150% so I thought-"I wonder what will happen if I bring it down to 100%" Wow! Its now perfectly sized.Thanks all for trying to help.

Dave