My advice is to only change the width of your image. If you change both the width AND the height your image will look distorted so I always find it best to change one or the other. Also, if you only change the width, your height will automatically change perfectly and vice versa.

So your image code should already look something like this: <img src="http://urlhere.jpg">

You want to end up with something like this: <img src="http://urlhere.jpg" width="300"> You can always keep increasing or decreasing the number until it looks the way you want it to. You will have to do this for each image you want resized.