problems with downloading ios 9.2.1

ive tried to download the new update but for some reason it goes to a black and white apple screen and a line to show how much its updated ,but it only goes to half way they shuts down and opens with "hello, slide to set up" then answer password and then says "update completed ,your iphone was updated successfully . There are just a few more steps to follow and then you've finished, continue" Then goes to apple screen the "slide to upgrade" and then password thing and then it will repeat the whole thing again but it will let me turn my phone off. Ive been doing this for 3 days and nothing has happened but repeating the whole cycle over and over again ! please help!!!!!