With WordPress, you’re almost sure that there will be a new version available at least every 2 months (averaging total new versions in a year) and for many, upgrading is still a night mare. Although this article doesn’t get into how to upgrade, which is explained by WordPress itself , it specifies the checklist that you must go through after each upgrade to ensure that everything is indeed alright.
Check your .htaccess file
This is the file that resides in the root directory and contains rules for your permalinks, your cache files, 301’s and a hell lot more. You do not want to mess with this one, so better check if it is still there in the root folder.
Compare wp-config and wp-config-sample files
Compare them both to see if any new additions are made to the wp-config-sample.php files. If yes, add them to the wp-config.php file (but don’t remove anything from this file, Sky will really fall on your head unless you know what you’re doing)
Check your file permissions
Users who upgrade their WordPress using Fantastico will find that all their files and folders will be set to 777 after the upgrade is complete. You do not want this to happen as that is a serious security risk. You can either manually change the permissions (generally used perms are 644 for files and 755 for folders) for each file and folder or ask your host to do so. Most hosts have tools that can reset the permissions to required levels with one click.
Check if web pages are working fine
Here, you may want to clear the cache (if you have) to see if the web pages are working without any issues. With cache, you’ll see your web pages running on old wordpress package and hence will not see any errors that ‘may’ have caused by the upgrade.