Change SPSite URL

To change URL of site you should run this script:

$site = Get-SPSite http://portal.contoso.com/sites/burek

$uri = New-Object System.Uri("http://burek.contoso.com") 

$site.Rename($uri)

After this change there is possibility that your site would not be accessible through new URL so you need to run Full Crawl on your Farm.

After Full crawl is finished site will be accessible through new URL.