Reinstalling KitKat after upgrading to Lollipop My Asus Google Nexus 7 has failed completely after upgrading to Lollipop from KitKat 4.4.4. 

Now the tab can not handle running more than one app at a time and frequently hangs requiring power shut down and restart. Can some one detail how KitKat 4.4.4 can be reinstalled? The tab worked marvelously earlier.
You can use this nexus-7 link to get started. There are nexus-7 developer forums where you can look for rom (other OS) to install it on your nexus-7.

Also,  you can install cynogenmod 12+ which is modified lollipop version of Google's Android OS. CM12+ is lot smoother in terms of performance and also has many features like themes and audioFX.

Please note - While installing anything on your phone voids the warranty of your phone.
Also, remember to follow each and every step as described in forum. Otherwise, there is a chance that phone will get bricked.
So, please be careful.