I have found the "Sunway" website I think... oddly enough at www.heywell.net
I personally cannot find any sort of firmware updates there. I would encourage you to look since I don't own your product but something seems very fishy to me about this company.... for one the website doesn't equal the name of the company and two the pictures of their products look eerily similar to other products. Again, I DO encourage you to peruse the website.
I bought an mp3 player off of eBay that is very similar to the iRiver iFP-790. It has the brand name "Sunway" on the front of it. It's acting up and I'd like to upgrade the firmware to see if this fixes the problem(s). Unfortunately, there is nothing in the user manual about web sites to go to for technical support/firmware upgrades and there are no contact numbers. If you think you have one of these players and know how to get technical support for it please reply! I'd hate to have to throw out an otherwise functional mp3 player simply because I don't know where to go to get the firmware flash file.