Thank you very much for your post, Karina!
I am afraid that it is not possible to Import/Export diagrams between JUDE/Community users.

In JUDE/Professional, there is a merge feature that you can merge JUDE files.
Also the main purpose of the use of JUDE/Server is to support UML model management (i.e., by various team members) for models produced by JUDE/Professional to let team members work on shared models together.

You can evaluate JUDE/Professional for 20days!
http://jude.change-vision.com/jude-web/getEvaluationLicenseButton.do

Also we have been serving Academic price for JUDE/Professional.
http://jude.change-vision.com/jude-web/academicprogram.html

Regards
-Satomi