Edit Posts with [IMG] tag

[GSX-Racing]

Hello again.

Here is my problem. Someone uses the [ img ] tag to display an image in their post. However the image is really big so as a moderator I want to change the [ img ] tag to be a [ url ] tag.

When I go to edit the post, the image is showing up in the edit box without any tags. I can only delete the image by clicking on it, then hitting delete.

How can I change the [ img ] tag to [ url ] in the edit post area?

Thanks