I'd greatly appreciate a response on the following question relating to site migration and SEO impact. Here's some background on how my domain name and site is currently configured:

My domain name provider has the following settings:

• host name @ is an A NAME record and points to IP address x.x.x.x
• host name www is an A NAME record and points to IP address x.x.x.x
• sub-domain host name new.example.com is an A NAME record and points to IP address x.x.x.x

My hosting provider has the following settings:

• host record @ is an A NAME record and points to IP address x.x.x.x, folder home/public_html/old
• host record www is a C NAME record and points to example.com
• sub-domain host record new.example.com points to home/public_html/new

I want to:

• point the domain (example.com AND www.example.com) to the content hosted under folder home/public_html/new, which is currently the content directory for new.example.com
• retire the content hosted under folder home/public_html/old
• retire the sub-domain host record new.example.com

I believe the easiest method of doing this, is: removing the sub-domain host record new.example.com; and changing the following line in the .htaccess file in home/public_html from

# Change 'subdirectory' to be the directory you will use for your main domain.
RewriteCond %{REQUEST_URI} !^/old/

to

# Change 'subdirectory' to be the directory you will use for your main domain.
RewriteCond %{REQUEST_URI} !^/new/

But I don't understand how this will impact my SERP - ideally, I'd like it to remain the same.

Research on this topic resulted in the following Google page, which was no help, and this related StackExchange question, which suggests that this should not affect my SERP (at least, not permanently). But I wanted to make certain with a more specific example, and hopefully contribute to the community at the same time.

I'd appreciate any feedback on this. Is there a better/recommended method to migrate sites this way? Is there an SEO impact?