Mastering the UI / Hotbars
The shape of each hotbar can be changed by selecting System > Character Configuration > Hotbar Settings > Display tab > Hotbar Display Settings.
Check the box next to the hotbar you wish to change and select the desired shape.
Alternatively, you can also change the shape by directly right-clicking the number of a hotbar displayed on the screen or using UI Element Settings in the HUD layout menu, accessed via System of the main menu.
Try out different shapes and layouts to find what best suits your play style and preference!