HTC EVO 4G SD microSD card

The device supports up to 32GB microSD memory cards, 2.0 SDHC compatibility.

To Insert/remove microSD card:

Ensure the device is powered off.

Next, remove the back cover of the device,
and then remove the battery.

See diagram on data plate under battery:
Raise red tab (1), microSD card will pop up.

Insert/remove microSD card in slot (2),
(use fingers, tweezers, or pencil eraser)

Close red tab (3) Replace back cover.

To view SD microSD card: connect the phone to the computer using the USB cable.
When prompted, choose Disk drive mode from the on-screen prompt.

Source: http://www.htc.com/us/support/evo-sprint/help/storage-card