How to make a panel to remove or add objects by user control object's calls

Question

I am writing a handheld program on CE 5.0 platform. There is a FormMain which contains a panel object, panel1. Once the FormMain is loaded the User Control Object, mainPanel will also be loaded into panel1. The mainPanel has a button, Entry. When user clicked the button, the mainPanel should be closed and other User Countrol Object, entryPanel will be loaded instead.
My question is how I can write some code on Enrty_Click method to trigger the FormMain.panel1 to remove the mainPanel and add the entryPanel instead.