Delete old theme and start over fresh…

I have decided to post my own topic here because of so many varying answers.

First time I’ve had to do this.

I would like to update to a new theme and totally delete all of the old theme files and start over so when I install the new theme, I won’t get any old pages or plugins or CSS incorporated into the new theme. I know WordPress will try to incorporate any old pages, plugins or anything old into the new theme you are installing. I don’t want this.

How do I completely clean house before installing a new theme so I don’t get any unwanted old content incorporated into the new theme? What files do I delete and in what folders do I start cleaning house?

I do know that I need to deactivate the old theme then reactivate a different theme first. Then, go back and click delete on the lower right corner on the old theme details page. I also know that I need to deactivate and delete ALL existing plugins from the site, the go back and reinstall the plugins after installing the new theme, I’ve been told.

Then what do I do?

Should I delete ALL old css style sheets too?

Where do I start deleting old pages? Do I need to ftp in and start deleting all contents from the wp-content folder? Do I leave all folders in tact but just clean all the folders out?

Should I clean out other folders too? Should I clean out the wp-includes and wp-admin folders too? Do I delete the whole folder or just clean the folder out?

Thanks in advance for any detailed instructions on how to go about doing this correctly! Most posts are vague and very differing on this subject.

Sorry for long post, just wanted to explain in detail.

Thanks!

Kevin