If you have EROM CID52 no need to update via SEUS to last firmware, because can use CID53 Firmware into CID52 Phone - Top Sony Forums


If you already upgraded with SEUS read here: Flash K800 CID53 with K810 software CID53 (for begginers) - Top Sony Forums

Now I use K810 R8BF003 version ( I flash only Main without File System ), but have only english menu, because haven't File System Mediterr for my region, in download section is only K810_R8BF003_FS_TELEF_GEN_RED53