Thanks Jason and George for details.
My requirements are like suppose if on my site theme1 is selected (consider https://websitedemos.net/love-nature-02/ these theme is selected and it has all default content and pages which came along with theme) and then after after using site for few days I want to change theme, let’s say to https://wpastra.com/templates/outdoor-adventure-02/ (Which have some new pages and different layout)
Then by default when we change the theme, it just changes the style and keeps old pages and content only
But suppose if i want import the pages from new theme and overwrite my old pages and content, Is there any way to manually do this?