how to upgrad your website

Keeping your Drupal site up to date.
there will be minor updates to Drupal core. If the release is designated as a security update, you should apply the update as soon as you can. Otherwise, you may choose to apply the update at any time to receive the bug fixes it contains. There are also major release upgrades; these you may want to apply so you have all the new and powerful features.
Whether or not you apply a major release upgrade is highly individual to the person responsible for that decision. Upgrading to a new major version usually requires a significant investment of time and work, as a lot may have changed between versions. If everything is working great for you, and you don't want to add any of the new features, you may decide to stick with your current major release of Drupal.
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When to upgradeUpgrade your website.

when it is at its quietest point in the day (ie. midnight). This is because your website will not be accessible to your visitors while you are upgrading.
Keep up to date on security announcementsIt is strongly recommended that you always keep your Drupal site up to date with the very latest minor release available, to remove known security vulnerabilities and existing bugs.
Following are some of the most common ways to stay informed:
•Your website: Via the Update manager (Drupal 7) and Update status (Drupal 6). Drupal can check for the latest release of core and any installed modules and themes. For more details visit the Update manager (and Update status) page.•Security Announcements: •Security advisories page: All security announcements are published to this page•Security newsletter. Log in, go to your user profile page and subscribe to the security newsletter on the Edit > My newsletters tab.•Security advisories feed: You can subscribe to the RSS feed of the Security advisories page.