Hello,
I want to update KMymoney to the newest version. I m using linux, how can I do that without deinstalling the prog.

Use the latest Linux appimage.
You can use the appimage without uninstalling the installed version.
You can now use either the old installed version or the new appimage.

Here is a link to the latest Linux 64bit appimage.
https://binary-factory.kde.org/job/KMyMoney_Stable_Appimage_Build/

There are instructions on the KMyMoney website howto download and install an AppImage as well.

As I posted a few days ago, I had very good success installing KMyMoney from the repository (sudo apt install kmymoney) but when I use the AppImage, the results were spotty. Specifically, under Kubuntu I am able to update stock prices online. Under (plain) Ubuntu I cannot update quotes. On a lark, I tried installing from the repository, but then running the AppImage. No joy. YMMV. Please share your experiences if they help.

Installing a package called kio (or similar, I am not an ubuntu expert) may solve that problem. It's a known issue that it is missing from the AppImage binary but needed. Kubuntu has it installed, so that is why AppImages are running there just fine.