I just installed the latest version 2.7.14 on OSX over the old version. When opening electrum it tells me that my trezor wallet contains multiple accounts, it should not. I don't know why it is telling me that ...
I don't know how to proceed. I might find an older version and install it before opening the latest version to make sure nothing important is lost.

I can also absolutely not lose my transaction history from the old version for example or names I have given to addresses... I guess my old version was something like 2.6.x ..  is there a risk that I will lose anything whatsoever?

Solved: After backing up the wallet, I answered to split the wallet. It created two new wallet files  wallet.0 and wallet.1. I answered not to delete the old wallet file, as a result the question to split the wallet came up every time I opened electrum so I moved the old wallet out of the folder.
All functionality is available as far as I can see. Initially the "Addresses" tab was gone but it can be brought back easily from the menu. Trezor was recognized.