you can update online, from 2.6 it might go to 2.7 and then to 2.8 It reboots a few times.
In the System Information there is a version section.
Click on those arrows and it will update.
Since there are major changes, take a backup of your config, do a clean install of 2.8 and then restore your config. Also, uninstall packages you have, you can re-install them later on 2.8
Same here – just updated my pfSense from 2.7.2 to 2.8.0 without uninstalling any packages. Running on Protectli VP2420.
Sharing same experience.
I really don’t understand what people are trying to achieve by chiming in here with a one-liner like, “I updated my box without any problems and without uninstalling any plugins.” Especially since they don’t even provide any information about which plugins they are using.
I suppose it’s great for them if they didn’t encounter any problems despite ignoring the recommendations of the pfSense developers, but it’s definitely not a good general recommendation for others. Above all, it won’t help anyone who wasn’t so lucky and did run into issues as a result.
I hope that anyone who prefers to take the YOLO approach at least backs up their configuration before clicking the upgrade button! 
Happy upgrading! 