• Minimal supported version seem to be 3.0.x, on jquery's website it says that 1.x and 2.x no longer receive patches.
• Upgrade guide: https://jquery.com/upgrade-guide/3.0/#overview
  • It involves first upgrading to 1.12.x and then jump to 3.x
  • There’s a jquery migration plugin to help: https://github.com/jquery/jquery-migrate

On the 3.0 release blog post they mention that it was created with backwards compatibility in mind, and that there're just a few breaking changes.

As a side note: IE6-8 support was dropped :)