VB.NET Windows Forms Textbox Scrollbar

Question

I have been trying to solve this problem for past two days., Tried a lot and looked everywhere but could not get solution. What I would like to do is expand the the hight of textbox programmatically , when the text inside a multilne textbox fills up the entire text area. so probably i need to captue an event when the lines wrap or captrue an event when the scrollsbars are enabled ? I do not know what to do to solve the above problem ? please advise.