The last firmware we released for ESP was version 0.9.2 if you have an older version you can follow the (just updated so maybe you need to wait a little ) instructions in the firmware update guide near the bottom.
If you are in a hurry here is a screenshot:
If you already have the latest version but for some reason you still want to upload the firmware, you can force by clicking the info button (top right) on the setup screen that you find when conected to your kit in [setup]( Link mode:
And activate the Force allow firmware update
So you will be asked for the firmware file.
Hope it helps!