send sketch from web panel using HEX file

Hi everybody,
This is my first post and I hope to not break any forum rules !

My question is: somebody knows in which way is possible to upload the hex file using web panel ?
In my case this option is only available if I insert the micro sd card and copy on it the file to upgrade openwrt image. In fact in this case I received two messages:

ATTENTION!!
This will erase everything stored on the Yún and update the whole system! Back up any custom files on your Yún before proceeding!

of course I skip it and then

Upload sketch
Select a .hex file (compiled sketch) and upload it on the microcontroller of this Yún.
For more information about how to obtain the .hex file of your sketch, visit this page.

Thank you so much for your helpful
Cristiano