You can upgrade to version 2015 from here; please note that version 2015 will not be released for at least a couple more days.  http://www.pcblibraries.com/products/upgrade/

These details will be released later today.

Tom,

Could you please give me an information how and at what cost an upgrade from 2014 to 2015 can be done?

For future releases, do we always have to purchase a new upgrade to a new version, or is there also a possibility to order a "maintenance" which includes upgrades?

Due to several bug issues we had to temporarily remove it to get the new V2014 releases out without holdup due to one buggy feature.
However, it will reappear in the V2015.01 release this coming weekend and it finally works perfect.
 
If you have a V2015 license you can download the 2015.01 pre-release is available from here:
https://www.pcblibraries.com/Downloads/FPX!Library_Expert_2015-01_Pro.asp

NOTES:

1.You must be logged in to download. So before you select the download link (above) “Log In” 1st.
2.This build was last updated a couple days ago (there are newer fixes in and more to come this week)
3.You will need to have either an Evaluation License activated, or if you are running the HASP SL/HL key, it needs to get updated with the 2015 version

Here are the new Altium import instructions:
http://www.pcblibraries.com/products/fpx/userguide/default.asp?ch=401 

We have a new 6 minute Library Expert V2015 video which highlights the new Altium interface:
http://www.pcblibraries.com/products/fpx/userguide/default.asp?ch=100