You can upgrade any version from Group-Office. For some versions it’s necessary to do it in steps:
2.18 can upgrade to 3.7.55
3.7.55 can upgrade to 6.2
6.2 can upgrade to 6.3
6.3 can upgrade to 6.4 and so on. Every major release needs to be upgraded to the next from 6.2 and higher.
Make sure your system meets the System requirements.
Needless to say, but always make a backup before upgrading.
You can find the change log here:
Release notes are posted to our blog: