Wanhao Duplicator i3 firmware update - where and how?

Hello,

I am new to 3d printing and have a Wanhao Duplicator i3 printer and using octoprint.

Printing works fine, no issue with that, but octoprint says that my firmware is unsafe due to the "thermal runaway protection".

Here I am a little bit stuck. I want to update my firmware, but I can't find one (I got google results for the i3+) and I don't know how to flash it...

Have anybody a url where I can find the firmware and a little howto and/or documentation how to flash the firmware?

That would be really nice.

Thanks and regards,
easy.