I'm not sure I understand the question.

It seems to me like you have an UltraDockManager on your Form and one of the controls which is docked as a pane is a .NET GroupBox control. You would like to change the height of the pane which contains the GroupBox, but it always remains the same height. Is this correct?

If so, it depends on where the pane is docked.

If it is floating or docked on the top or bottom and it is by itself (not part of a group), you would want to increase the height of the DockAreaPane, like so:

DockableControlPane controlPane = this.ultraDockManager1.ControlPanes[this.groupBox1];
DockablePaneBase dockAreaPane = controlPane.DockAreaPane;
dockAreaPane.Size = new Size(dockAreaPane.Size.Width, newHeight);

If it is docked on the left or right and it is by itself, you cannot change the height of the pane, because the pane is docked to take up the entire height of the UltraDockManager's container.

If the pane is part of a horizontal split group and you want to change the height, you would set the Size of the pane directly, which indicates the Size of the pane relative to the other panes with which it must divide its space:

DockableControlPane controlPane = this.ultraDockManager1.ControlPanes[this.groupBox1];
controlPane.Size = new Size(controlPane.Size.Width, newHeight);

I hope this answers your question. If not, please provide more details about the nature of what you are trying to accomplish.