problem with update (September 2015)

I've tried to update to the new OS on my ipod. (On the back it says it's Model A1509) It says I've nearly completed but have just a few more steps. It now says "> slide to upgrade" but it won't slide on the touch screen. The screen is working as I just touched "continue" a few minutes before. Its the current upgrade (sept 2015) and I was using wifi, not itunes.

Any Ideas?

Thanks