How to make tumblr banner a gif?

On the tumble iphone mobile app I see people with a gif as there like top banner/header photo. I just can't figure out how to do it. On the phone that is. So if you know I would appreciate any help, thank you ^.^

Instructions

1 Click "Start" and then click "All Programs."
2 Click the folder labeled "Accessories."
3 Click the link labeled "Paint." The Paint application will open.
4 Click the "New" option from the top menu bar, and then select "Open." A file selection dialog box will open.
5 Navigate to and click on the GIF file to convert. Click the "Open" button. The GIF file will open in Paint.
6 Click the "File" option from the top menu bar.
7 Click "Save As." and then click the "JPEG (.jpg.jpeg, .jpe, .jfif)" option from the
"Save As Type" drop-down list.
8 Type a name for the new JPG file and click the "Save" button. The GIF file is now
converted to the JPG file type.
9 Connect the phone to the computer according to the device's user manual.
10 Copy the JPG file to the phone device.
11 View the JPG image on the phone.

Hope this helps.