@misterlisty Youj can dowload images, like
https://software.pycom.io/downloads/WiPy-1.15.0.b1.tar.gz
or
https://software.pycom.io/downloads/LoPy-1.16.0.b1.tar.gz
This archives contain a file called appimg.bin, which you have to use for OTA.
The files system is kept during OTA, including boot.py and main.py