I want to update to Lollipop so I want to unroot. When I tried to update, obviously it says it can't work. The weird thing is that I don't have root access anymore. So what do I do? I used towelroot.
Reflash the 4.4.4 stock ROM (backing everything up first, of course). There's something that was changed when the phone was rooted that can't be changed without root - and that the update is checking. It could be from rooting, it could be something you did or it could be something that a rooted app did.
Did you have a custom recovery installed, and did you remember to uninstall it before you unrooted? I made that mistake when the 4.4 update pushed.
If that is your problem the easiest way to get back to stock is flashing with ODIN.