The correct way of handling variable DPI settings is not to detect them and adjust your controls’ sizes manually in a switch statement (for starters, there are far more possibilities than those you show in your sample if statement).
Instead, you should set the AutoScaleMode property of your form to AutoScaleMode.Dpi and let the framework take care of this for you.
Add the following code to your form’s constructor (or set this property at design time):
this.AutoScaleMode = AutoScaleMode.Dpi;
Although you might prefer to use AutoScaleMode.Font. For more information on automatic scaling, see the MSDN documentation.