Why we need to upgrade WordPress:
In Modern time, all world being using the online web services for own company sales and these website needs upgradation time to time to keep going live. Old version site and old code have a risk of malwares and hacking, so WordPress provide time to time latest version of core package and notification in the back-end of wordpress with security upgradation.
How to upgrade core WordPress:
If you are looking for to upgrade your wordpress core files then, you will need to follow the below steps and replace core folders carefully. These steps not only help to upgrade your wordpress website but also save your custom work of files and database.
1. You need to take a backup of your old files and database.
2. If you are not able to taking backup of your website due to large collection of files than only take a backup of database, some files like wp-config.php, wp-includes/languages/, htaccess, robots.txt and do not delete wp-content folder & its sub-folders in any case.
3. Now download the latest version of wordpress and extract zip file on your PC.
4. Replace only core file (wp-admin, wp-include, and other files on root of default wordpress) except mentioned in point 2 files.
5. Now hit the admin URL of website. After refresh you will get latest version of wordpress or may be ask for upgrade database.
6. Now check site front-end, which is ready with latest version of wordpress.
How to upgrade WordPress Plugin:
7. Go into the plugin section of wordpress back-end.
8. If any plugin have latest version, upgrade it but if your plugin have custom code then take a backup of those codes and upload at new upgraded plugin in same file or check what new changes have been included and take action accordingly.
9. If some plugin not in use anymore, delete that because large number of plugin slow don the speed of website and increasing the chances of hacking.
How to upgrade WordPress Theme:
10. If you are using paid and original theme without any customization then, you will not get any problem to upgrade theme. Just need to download compatible theme of wordpress latest version from your account and upload it on your website.
11. But if you are using paid or custom theme then you just need to change deprecated function of wordpress.