How to boot in download mode with a Zonda a450 Already googled this, no results, i tried with youtube video tutorial in which you supposedly boot your phone in download mode while holding the volumen down button and the power button, but it doesn't nothing.

I have a Zonda a450 with android 4.4, i want to boot in download to upgrade to android 5.
Okey. As described in the specs, the device has a Spreadtrum chipset (SC7731). There is no boot mode on SPD devices.

To flash a ROM, you need a file in the .pac format and use a flasher (ResearchDownload). 

You MUST install SPD drivers, otherwise the device won't be detected by the computer. 

As there is no download mode, just swicth off and plug the device by holding volume down or up.