Fps selection is also determined by the video format (pal/ntsc), if you change from one to the other you will see either 50fps/60fps, but they also dependent on the model and the shooting mode selected.
As long as you've done the update then you are probably in 4:3 format which does not allow 60fps in 4k. When selecting quality and frame rate you should see a 4:3 in the top right corner, tap it and select 16:9 and now 60fps should be available.
