First thing to do -
Create new web application on SP2013 Server where we are going to migrate the site collection.
1. Backup and restore SharePoint 2010 Content DB in SharePoint 2013 farm
2. Run "Test-SPContentDatabase" command to make sure that new environment has all components that SP2010 is using.
3. Database Attach: Run "Mount-SPContentDatabase" to attach the database to the web application in SP2013.
4. After successful mounting the content DB to web application, the site will be accessible in 14 mode.
5. Next, to upgrade the ite to 15 hive, navigate to SiteUpgrade.aspx page in Site Setting of your site collection.
6. Click on "Upgrade the Site Collection" button.
7. During upgrade, the progress bar will be displayed.
8. After completing the progress bar, site collection must be accessible in 15 mode.