Here is a link to the Legacy section, which has links for the two different 8830s. Choose the proper one and follow the instructions and you should be all set.
Check the yellow sticky at the top of the legacy section for the latest OS for your device. The OS is device specific meaning you must install an 8820 OS, an 8800 or 8830 OS will not work.
In addition, the instructions on how to doit are there s well. Follow them EXACTLY and have patience. It can take an hour or longer to complete.
AND, make sure that you do a complete backup beforehand, just in case you need to recover.