How to enlarge the button size of WF DateTimePickerAdv?
The WinForms DateTimePickerAdv control does not have direct support to enlarge the Up/Down button size. But you can customize the Up/Down button size by adjusting the value of Font or Size properties. Refer the below code for your reference.
C#
//Using Font property.
dateTimePickerAdv.Font = new Font("Microsoft Sans Serif", 14.25F, FontStyle.Regular, GraphicsUnit.Point, ((byte)(0)));
//Using Size property.
dateTimePickerAdv.Size = new Size(276, 50);
VB
'Using Font property.
dateTimePickerAdv.Font = New Font("Microsoft Sans Serif", 14.25F, FontStyle.Regular, GraphicsUnit.Point, (CByte(0)))
'Using Size property.
dateTimePickerAdv.Size = New Size(276, 50)
Output:

Sample: View sample in GitHub.