EspoCRM can be upgraded to the latest version by the following steps:
To check your current version go to Administration > Upgrade page.
Go to the upgrade page https://www.espocrm.com/download/upgrades/ and based on your currect version download needed packages.
Create a backup of your EspoCRM files and data before upgrading. Follow these instructions to get it done.
Go to Administration > Upgrade. Upload and install one by one upgrade packages.
You can check whether you have the latest version at Menu > About.
You can also run upgrade via command line interface. You need to execute the following command from EspoCRM root directory:
php upgrade.php /path/to/upgrade/package.zip