update problem

hii!
first sorry of my english!
i have installed stock rom flashable zip 5.0.1 from this forum. i get an upgrade to 5.1.1 i download it and press update the device turn off and go into recovery and nathing hapend still i reboot system by my self(i have multi rom last version, the stock rom is set as internal rom)
hoe to fix the problem? Thank's