How often have you made the perfect banner, but then realized it was too small or too big for you to use? How often did you find the most amazing picture, but it ended up not being the correct size so you couldn't use it?
I know this happened to me countless times, and I know how frustrating it can get, and therefore decided to create this tutorial, that will teach you how to resize your image using Photoshop (Thanks Elien for giving me the idea btw ;P)
First off, open your PS and the image you wish to resize, then at the main menu, go to Help > Resize Image > Choose Online/Print (depending on the fact if you wish to print your creation later or not).
Now, choose the width/height that you want - but only one of them, because the program will automaticly choose the other optimistic resultion to match your selection. If you're not sure, you can always ask the program to Preview your new picture. Click Finish, and you're done!
As simply as that ;)