I changed to another motherboard.
How do I force Ubuntu to renew its knowledge about hardware and install proper drivers?
Linux does not keep any persistent "knowledge about hardware"; everything is auto-detected during boot – or when you plug the device in (for USB and such). All drivers are loaded dynamically, and 99% of them were already installed as part of the kernel. (The other 1% are proprietary video drivers, mostly – and Ubuntu takes care of them.)
Short answer: There is no need.
If you are using a kernel provided by your distribution (ubuntu) then there is no need. The Linux kernel loads modules dynamically, and if there is any change, it will just load the appropriate module. If it can't, it means that module is not compiled into the kernel.
If you have a custom compiled kernel with minimum modules compiled, then you should recompile it (but I guess this is not the case).
If you have been playing with Xorg configuration, then you should check that it is using the corresponding module for your video card. But if you did not touched