How should I handle Extension Update

Hi Everyone,

I have some issue about the extension upgrade. When I made some change to the database, the will have some errors while I'm upload my extension. Such as Unsupported field change( Change:DataType). What should I do to update these field. Is that writing a upgrade codeunit? How should I write it and how it work? Sometime I will encounter an error saying "previous version have been published , please run Update cmdlet to upgrade". Is that also should be handle by upgrade codeunit?

Thanks in advance.