It is super easy to resize a picture with iPhoto if you still have that on your mac:
1) Go to file, then "import to library"
2) Select the desktop, then import the image
3) Once it's imported, go to "share" and then "email" and email the picture to yourself. This will resize the file while keeping the actual dimensions. Open the email and save it as a different name so you don't get it confused with the first.
If that doesn't work, let me know
1) Go to file, then "import to library"
2) Select the desktop, then import the image
3) Once it's imported, go to "share" and then "email" and email the picture to yourself. This will resize the file while keeping the actual dimensions. Open the email and save it as a different name so you don't get it confused with the first.
If that doesn't work, let me know