Upgrade from 6.3 to 6.5

Adobe documentation captures all the scenarios for the AEM upgrade. Please refer to it at [1]. On a high level, the changes are

1. Upgrading the AEM instance - you can do either an in-place upgrade or fresh install approach based on your content size and
2. Upgrade your artifacts by compiling against 6.5 uber jar.
3. Test and fix any issues due to deprecated features/overlaid capabilities change.
4. From 6.4, as part of the sustainable upgrades process, there is a repository restructuring that can be done (not mandatory). Refer to it at [2]
5. Process on how to roll out the changes to production.

If this is hard, adobe offers a backward compatibility mode from 6.3 with which you can run a 6.3 AEM artifact on a 6.5 instance. Read more at [3]

Pattern detector is a mechanism provided by Adobe to easy identification of possible problems that will come up during upgrade by validating against deprecated features and overlays. Refer more at [4]

AEM 6.5 is compatible with Java 8. Refer to [5]

[1] - https://docs.adobe.com/content/help/en/experience-manager-65/deploying/upgrading/upgrade.html
[2] - https://docs.adobe.com/content/help/en/experience-manager-65/deploying/restructuring/repository-rest...
[3] - https://docs.adobe.com/content/help/en/experience-manager-65/deploying/upgrading/backward-compatibil...
[4] - https://docs.adobe.com/content/help/en/experience-manager-65/deploying/upgrading/pattern-detector.ht...
[5] - https://docs.adobe.com/content/help/en/experience-manager-65/deploying/introduction/technical-requir...