Unfortunately it is a common policy for resellers to cancel the warranty if the buyer upgrades the ROM. Several manufactures though allow upgrading for their official ROMs, but I am afraid this is not the case for Freelander, for which unfortunately I have not found any official ROM (at least not in Chinese). I am not sure what are the legal aspects of such policies. In any case there is a risk involved when upgrading a device that the device may be 'bricked', ie be rendered unusable if something goes wrong.
Now regarding the ROMs for the particular device, I believe I have found mainly two alternatives.
The first is to use a ROM from a similar Ainol device. The link for the ROM is http://pan.baidu.com/share/link?shareid=352175935&uk=420337580 (use Google translate to identify the download button which should be the second at the right hand side).
The update procedure along with some testimonials can be found on:
According to those testimonials, the only thing not working properly after the upgrade is the front camera.
The second alternative is to use one of the Cyanogenmod ROMs (10.2 or 11) for Allwinner A31 device. In the above links you can find all relevant information, along with whatever may go wrong.
I have not yet evaluated any of these but I will eventually as I own such a device and the existing ROM is nonsense. Please provide any feedback when available.