I am using a MDI form with my VB6 application. I have another form
called "frmesm" which is set as a MDIChild. However, I would like to
change the MDIChild during runtime to a diffrent form called
frmnewchild when I click on button "changechild", and make "frmesm"
not a child form?

I don't think you can change youVB application model between MDI and
separately-windowed at runtime.

Maybe you could make frmnewchild in an altogether different (non MDI)
VB project.  Then call the frmnewchild.exe command using the shell
command, just like you used to open the form in Access.