Remove user account in Android 5.0.1 on Galaxy S4
I have spent weeks looking for a solution to this and finally this post helped me! It was so far from obvious and it felt like Google wanted me to keep the account by force lol.

Anyway, what I did was go to Settings > Accounts > Google, clicked the account I wanted to delete, the Sync menu option opened and this is where I always got stuck. Through this, I realized I had to press and hold the menu button on the bottom left side of my S4 to get another menu pop-up with the options of canceling sync or deleting the account.

Finally! Hope this helped.