Inserting images in mailing
There are two issues going on here.  First, you have images that you attempt to resize, but they are appearing wrong for many recipients.  Second, you can't fix the images.

I can't answer the second issue without knowing your particular server environment.  I'm especially puzzled how you got your images up there in the first place but are having trouble now.

However, I can explain the first issue.  When you resize an image in the editor window, all you're doing is adding HTML parameters or inline CSS to constrain the images to a given height or width.  You have to trust the recipient's email client or webmail to carry out your instructions, though.

It's not uncommon for email clients to strip out the inline CSS that scales images, so that's what you're facing.  You're on the right track: get the actual image file to a size that is reasonably close to what you want, and then only trust the editor for fine-tuning.