Hi Pelldis,
As Andres correctly stated, if you would like to upgrade the device from 11.2 -> 12.1X46, you should upgrade to an intermediate release 11.4. However, it is quite difficult to get the 11.4 version unless you open a case with JTAC where they will have access to Junos archives.
Alternatively, you can upgrade the Junos from 11.2 -> 12.1X46D40.2 directly via Bootloader using USB storage as mentioned in the following technical documentation - https://www.juniper.net/documentation/en_US/junos/topics/topic-map/install-software-on-srx.html#id-installing-junos-os-on-srx-series-devices-from-the-boot-loader-using-a-usb-storage-device
Let me know if you face any difficulty.