The Riot has 4 torx head screws holding it together. I found that a 2mm straight tip screwdriver works well in removing these screws.
After you take the screws out, gently lift the top cover off. The volume control is a single part that is easily removed by lifting it straight up, and the power button removal is the same.
Now gently remove the entire assembly, being careful to grab the battery (on the left side) as soon as possible to keep it from damaging the connector, or breaking a wire (don't let the battery dangle by the wire !)
Gently remove the battery plug from the connector and place it aside.
The battery is 3.7V, 1800mAh - there is more information in the battery.txt file in the download link below.
If you're just replacing the battery, do so, then put it all back together, paying special attention to the battery temp sensor. Be careful not to pinch the wires, or break the connections on the board, or the player will not work !
Here is a link for the Riot with battery recalibration information, firmware updates, manuals, etc.
Here is the Mediafire link: Rio Riot Files.zip *** UPDATED/Checked 3/12/2017 ***
This link has the 1.25 firmware update, Rio Riot Manual, new battery information, battery calibration information, the readme for the 1.25 firmware update, and some PDF files that I pulled from the almost gone Rio website - and the RiotReader beta that lets you pull the drive and use it in Windows!
If you're just replacing the battery, you are finished with the hardware part. Now go to the link above and follow the directions on how to properly calibrate the battery.
If you are going to install the HD as well, head to the next step.