Asus Eee Pad Transformer Prime TF201 Using Manual page 4

4. Prepare a MicroSD card. Unzip the compressed firmware file to the root
directory of the MicroSD card.
You only need to unzip the downloaded firmware file once before
launching firmware update.
5. With your Transformer turned ON, insert the MicroSD card into the
MicroSD card slot.
6. An exclamation mark
appears in the notification
area. Tap the mark.
7. A System Update File
Detected message appears.
Tap the exclamation mark
to start firmware update.
We recommend you to connect the power adapter to your Transformer
before firmware update.
8. Select the update file you download from the ASUS Support Site and tap
OK to continue.

ASUS Transformer