Using the Image Editor:
You can crop, resize, and edit your images from directly inside of the Image Manager. First click on the Image Manager icon in when editing a page. Click on the image you wish to edit and then click on the Image Editor button.
From here you can perform a number of edits to the picture.
Opactiy - If your picture is in a file format that supports transparency (such as PNG or GIF) you can use the slider to make the image transparent. A opacity of 100% will be completely solid and an opacity of 0% will be completely transparent (and thus invisible for all pratical purposes).
Resize - You can use the width and height sliders to change the width and height of the image. For small changes, click the left and right arrows and for larger changes click and drag the slider. If you wish to keep your height and width proportional, ensure the Constrain proportions option is checked.
Flip - You can use this to flip the picture horizontally, vertically or both.
Rotate - You can use this to rotate the image. You can rotate 90 degrees, 180 degrees or 270 degrees. This can be useful for images that were scanned incorrectly or pictures that were taken with a camera held sideways.
Crop - Once you click Enable Crop a red box will appear in the corner. Click, drag and resize the red box to highlight the area of the picture you wish to preserve.
Restore Image - If you decide you want to reset your image back to its original state, just click this button.
Save As - By default _thumb will be added to the end of the name of your image file. You can change it to something else if you wish.
Once you have finished with your edits, click
Save to create the new file. You can now insert this file from the Image Manager just like you would with any other file.
Click
here for article on how to resize pictures using Paint and iPhoto.