Just a quick info: as part of our testing we have auto-upgraded 2 sites from b2evo version 5.2.1 to 6.7.6.

It all wen flawlessly. The only things to pay attention to are:

• replace the old .htaccess with a copy of the provided sample.htaccess
• remove custom configs you might have done for multiple domain handling, as b2evolution now handles almost everything in the core