Migrate the whole sample site from a sub domain into the main domain

See Moving_WordPress.

Hi esmi:

I posted another post so that the question is fixing on more detail on my situation , please help me out on here:

https://www.ads-software.com/support/topic/the-safer-way-to-migrating-a-site-yet-maintain-its-trial-copy-in-same-domain?replies=1#post-2581087

Thanks a lot!

Please stick to this topic. Duplicate topics (like yours) are deleted on sight.

crap, how am i going to get the stuff I posted on that deleted post?

and the heck I can not edit this post, ok, post as reply then in this case:

Hi, everyone:

I was asking migration of site, but realize it may not be the situation after I read the article provided by esmi.

My situation is like this:
For example, my domain is https://www.abc.com and there is a existing WP site on the domain, I want to change the whole WP site.
So, I have a trial WP site established on https://www.abc.com/trialsite/

I wonder how can I transfer the trial site seamlessly (as much as possible, as less lag as possible) to replace the site under the main domain? meanwhile I want to maintain a backup of the original domain old site.

I wonder if there is a detailed instruction beside Moving_WordPress page that apply to my situation?

Thank You All in advance ??

Is the site on the main domain also using WordPress?

Yes it is ??
Any possible solution? ??