What I found out:
1. You can't upgrade your tekkit server by just downloading the new one and using one of the manny tutorials online BECAUSE the new tekkit pack is missing a holle bunch of Mods.
2. once I did manage to merge the New and the old ... The new client was incomplete :| ... MC itself was trowing a heap of missing-mod-errors.
Concluding: You can upgrade it but only if you are a Nerd (I managed it by nerding it up) I would recommend a big sigh at tekkit for failing on the updates... what's tekkit if you can't keep your world? Just finished a giant city and now it won't let me continue if i wants to upgrade? Tsk
(ye ye still, the lord be praized that tekkit excists at all ^^ )