Have a look at the matrix , you have the answer right there
Regarding your second query -> first we have to upgrade all of our edge gateway to 6.3.6 and then upgrade NSX Manager
NSX Manager followed by edge upgrade is the only possible way.
Thanks for response ,yes,I seen VMware compatibility matrix for upgrade path .
My key concern was if I upgrade NSX Manager to 6.4.x,will it backward compatible with existing running edge gateways with 6.2.8/6.3.6? Because I don’t get into edge issues due to compatibility issues with NSX manager which will be upgraded to 6.4.x
Yes, your edge versions are compatible with NSX 6.4 . However i recommend to upgrade the edges ASAP once the manager upgrade is completed.