Error Sideloading Android L

Hello I am trying to update my nexus 7 (2013) wifi to android 5.0 with adb sideload. I get this error:

Finding update package... Opening update package... Verifying update package... E:footer is wrong E:signature verification failed Installation aborted.

I have the file (razor)it is a .tgz file so I entered into the command prompt (i opened inside SDK platorm-tools) "adb sideload beaverlog.tgz" and it got that error. [beaverlog is what i named the file.]

PLEASE HELP!!!!!!!!!!!!!!!!