LTE MPIM firware upgrade

Here the procedure:

https://www.juniper.net/documentation/en_US/release-independent/junos/topics/task/operational/lte-mpim-firmware-upgrade.html

Download the firmware:

From the main JunOS sw download page:

https://www.juniper.net/support/downloads/?p=srx320#sw

  Click on the Right Corner 

or directly:

https://www.juniper.net/support/downloads/?p=junos-srx#sw

the JFirmware package (Sprite FW package 17.5.506)

And here the release notes for JunOS:

https://www.juniper.net/documentation/en_US/junos/information-products/topic-collections/release-notes/15.1x49-d120/index.html