About Download Mode:Download Mode is a state your phone can be in that allows you to flash firmware through Odin or other desktop software.
When in Download Mode, you will see a triangle with an Android image in it and it says "Downloading..."
If you are stuck on the 'Downloading..." screen, you can just remove and re-insert the battery then power the phone back on.
If you are flashing firmware while in download mode, then you unplug it or remove the battery, your phone probably won't turn on any more.
Download Mode is essentially the same as Bootloader Mode.
How To Access Download Mode for Ace 4 :4 Ways to do access download mode for Ace 4
1-Button Combo
Turn off the device.
press power button and select “power off” or press and hold power key for about 5 or 6 seconds.
You can also remove the battery for a few seconds; of course, then reinsert the same.
Up next, press and hold power, volume down and home buttons at the same time.
Don’t release the buttons until the Android Logo with the Warning message displayed.
In the end press Volume Up in order to confirm that you want to enter download mode.
There you have it; you can now safely connect your Ace 4 with your computer for completing further step by step procedures.
4-CMD/Terminal
a-Install ADB
c-Enable
USB Debugging on your device and plug it into your computer via USB cable.
d-Open CMD (windows) or Terminal (linux/mac). To open CMD, hold windows key, then press R, then type cmd.exe and press enter.
e-Type adb reboot download