How to downgrade Nexus 7 Tilapia variant to Jellybean?

I tried doing the instructions from the developers page (new user so i cant post a link)

but I always get this error when I execute flash-all.bat

sending 'bootloader'...
okay [ 0.500s]
writing 'bootloader'
FAILED <remote: <invalidState>>
finished. total time: 0.734s
rebooting into bootloader...
Okay [ 0.20s ]
finished; total time: 0.21s
sending 'radio' <43814 KB>...
OKAY [ 5.428s]
writing 'radio'
Failed <remote: <invalidSize>>
finished. total time: 5.460s
rebooting into bootloader...
FAILED <command write failed <unknown error>>
finished. total time: 5.004s
archive does not contain 'boot.sig'
error: out of memory
press any key to exit

I am currently on lollipop and I want to downgrade to jellybean so I downloaded the razorg 4.3.1 image. Any chance its wrong?
Here is what my device says on bootloader
fastboot mode
product name - tilapia
variant - tilapia
mw version - pr
bootloader version 4.23
baseband version- na
signing - not defined yet
lock state - unlocked

I am new to android because someone just gave this to me and I want to downgrade because it's too laggy. Anyone there who would care to give me a step by step instruction on how to do so? and please tell my what error I have made. Thank you