Your model is A6000-L Dual-Sim, and you can safely upgrade it to the latest version,
via full flashing by PC + USB cable.
Latest publicly available is version S061
Download :
A6000_L_S061_160727_8G_ROW archive pass: lenovo-forums.ru
Download also :
Flashing instructions
All needed tools and drivers are inside ROM archive.
Read carefully flashing instructions.
Use Win7 32bit for flashing, or WinXP. These OS have highest success ratio.
Disable all other tools like Samsung's KIES, Sony PC Companion, etc.
(They are known to mess with usb ports and interfere with Lenovo flashing tools).
b.r.
Alex