Had to change the My Site URL for a farm recently and for some reason I thought it was a lot harder than it turned out to be. There are 3 things you need to do:
- Change the Default Alternate Access Mapping (AAM) from whatever it is to what you want it to be, moving the existing URL to another slot in the Public URL field list.
The My Site service uses the Default AAM in the My Site Web Application to “manage” the URL’s in the service, so if you don’t change this first you will find SharePoint resets the changes you make in My Site Settings page. - On your User Profile Service Application settings page, click Setup My Sites – Change the URL in the “My Site Host” field to the new URL (the one you just changed your Default AAM to).
- In IIS on each server, open up the Host settings for the My Site web application and update the URL to the same one (It’ll still have your old one on it).
Tips:
- Don’t delete the old Default URL – either move it down the list of external URL’s or if you want everyone to go to the new URL set it up as an internal URL for the Default zone.
- Check and make sure you are indexing the new My Site URL in your Search Service (not the old URL)
- This process may not move existing sites – if you get stuck, Eric Fang has created some powershell scripts to manually convert them to the new URL: http://fangdahai.blogspot.com.au/2013/01/how-to-change-my-site-host-url.html
SharePoint Blog 
Hey Brad – do I need a DNS entry in order for my new url to show up in the address line when a user clicks on my About Me (mysite)? I have everything you state above however, when I click on my name->About Me, the url still looks like this http://servername:18215/Person.aspx instead of http://servername/mysite/Person.aspx
Hi Kim – I have updated the article (not sure why just modifying the AAM’s worked for me in that instance, because it should not have done so…)
Thank you for these very useful tips, especially about PictureURL parameter on user profiles. greetings from brazil.