You can check which version of WordPress you currently have installed by logging into your WordPress admin then clicking the 'Dashboard' tab on the left of the screen.
It's essential to know what version of WordPress you're using so that you know if it's compatible with certain themes or plugins you might install.
After you check wordpress version, you may want to update your outdated version of WordPress by clicking the update link that appears at the top of your admin screen.
Updating WordPress may render the current plugins and themes inoperable. It's a good idea not to update your version of WordPress unless you create a backup of the current WordPress posts, pages and database.