how can i change the boot screen resolution resp. the login screen resolution?
“boot screen” - do you mean the Grub screen?
no… if the pc is booting there is a ubuntubudgie logo on the screen … the resolution is always 1920x1080 … also on the login screen …
unfortunately nothing change … but the wanted resolution is not avalible with vbeinfo
if its not available in vbeinfo you cannot set the resolution. The problem is due to an incompatibility with your display (monitor?) and the information held in the kernel to display it.
its a 15" laptop … 1920x1080 on 15" is too mutch for an old man … 
so login is on 1920x1080 an to work on ist i use 1600x900 … so i search for an trick to use 1600x900 all the time …
I found this on Ask Ubuntu - helpful to set the resolution on the actual login screen?
Laptop does not start.