search online for custom roms for you device, and download zip file.
if there are no custom roms available for your exact model, you can port a rom made for a device with the same mediatek number and kernel number as yours (look at about phone for this info). Research on phones with your same mtk and kernel numbers, and find custom roms made for them OR their stock roms. search how to port roms for mediatek devices online. I successfully ported and flashed a ROM for my MTK device by learning how to do it online.