I don't know what these are in english: Tukivarsisarja, vahvistettu Passat 3B, A4, A6, Superb

Has anyone change those? Is it difficult to do?

I'm thinking of changing those, because my car doesn't run straight anymore. -> I have to steer.

And heard that this would help.

Not changed them personally, but the 100mm (roughly) bolt that goes through the top arms WILL be seized up solid if they have not been taken out and copper slipped before (thats the bolt you can see when you look under the wheel arch, just above the tyre), this will be a PITA to get out if seized, although if you are replacing the arms there is no reason why some heat can't be applied to help them come out - just keep the heat away from the strut as best you can.