Moving Blog To New Directory With New WP Installation

Not sure if this is the place for this question, but I cannot find the answer elsewhere.

I have a very long/old blog and the SQL database is getting full. I created a new directory and did a fresh install and pointed the URL to the new directory.

I created a subdomain that I plan on pointing to the old directory so readers can have access to the old site.

What files do I need to adjust with the subdomain URL in the old installation?