Hi Tony,
thanks for reply. It works.
At the old Installation (J2.5.x)
[list=a]At the backend I added a new menu-entry "Export" to my main-menu
[list=b][/list

]Then I hide the calendars, except this one i want to transfer. (this is, because I have single calendars for every year)
[list=c][/list

]Now, at frontend, I choose the export-menu-button and export the calendar-entries which are now not hided (e.g. 2015).
[list=d][/list

]I got an .ics-file with all entries an categories and saved it on my computer.[/list

]
At the new installation (J3.4.x)
[list=d]At the backend I create a new calendar. The entries where importet by file (the .ics-file i got).
[list=e][/list

]While JEvents import the entries, it also imports the categories as well when settings are made correct.
[list=f][/list

]After this I had all the categories and entries from old calendar transfered to the new installation.
[list=g][/list

]This workaroud I did three times for different calendars (2013,2014,2015) and everything works fine.[/list

]
I think this discription will help some other useres in the forum.
Kind regards
Wolfgang