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Joomla 2.5 can be upgraded to 3 X using the joomla updater in admin and if you have the ijoomla installer installed (found in the product download) then you can just press update and it will do it all for you.
My version of JomSocial is 3.2.1.5. It need not be updated.
I'm upgrading the version of Joomla to 5.2.24 to 3.3.6.
As I have numerous components installed, you can not migrate by administrative order of the panel.
My preoccupation with the migration of Jomsocial. I can not lose data. I have a community of 9,000 members.