I want to downgrade to KitKat 4 but cant

I have a Nexus 7 model, and i did find the instructions to donwgrade over this site.
But still I cannot do it, now with Lilipop 5.0.1 is crashing all the time when i try to open
a site on google chrome.

what else can i do please any help as i am going metal, i cannot do anything on my tablet
as keeps crushing all the time, reading mails does t open Facebook does it, trying chrome
browser does it too, and even when i try to use applications like google maps or calculator
it does again.

I want my Nexus Back on Kit Kat 4.4

Regards for any help people
G.D