RuneScape players had to adjust to RuneScape 3 throwing the interfaces into a state of confusion. However, it is still possible to revert to a setup that resembles much closer the traditional RuneScape experience.
This can be done by looking for the tab that resembles a cog. Double-click on that in order to access the options menu. On the options menu, there is a menu option lower down that says "select a preset." There, click the gold arrow to the right of those words to open a drop down menu. Scroll down and select "old school."
Then select to shrink the chat area, add the tabs that you need to access a lot such as clan chat, and make other changes. Then save it as a preset, either preset one or preset two. That way, you can always reload your preferred loadout, especially if you manage to mess up the layout and cannot figure how to undo the accidental change.