Log on to Admin Dash board , click on Dash board, Scroll down to bottom of the page, In the footersection  we can find the version of the Wordpress we are currently using

To upgrade word press  Intially Backup the your website(before making any change including data base and all files), if automatic update is enabled wordpress will automatically update to latest version  when a new release is available. else

1- Down load latest version from wordpress.org

2- Deactivate all plugin to prevent any conflict during update process

3-Upload the new Wordpress files to your server, replacing the old files (except wp-content and wordpress config.php)

4-visit admin dash board, if there any data base update neaded wordpress will promt you to perform them. 

5-Reactivate Plugins.

6- Verify the update(to  check every thing is working correctly)