For general information on upgrading EXOS, see How to Obtain and Upgrade EXOS
Note that the Summit X440-G2 and Summit X620 USB ports are not supported in EXOS 21.1. Support for USB ports on the X440-G2 and X620 will be added in a future release.
Update: In some newer firmware versions the "download image memorycard" command does not exist anymore.
In this case the upgrade can still be done from a USB flash drive, by issuing "install image /usr/local/ext/<firmware>.xos", however please be aware that EXOS will remove the image-file after issuing the install command, so if you want to keep the image on the USB flash drive, it's better to first copy it to the switch.
This can be done by issuing "cp /usr/local/ext/<filename>.xos /usr/local/tmp " to copy the file from the USB drive to the internal storage, and then run the install from the internal storage intead: "install image /usr/local/tmp/<firmware>.xos".