troubles with video-resolution

although i know how to change video-resolution i had some troubles when the image is flickering.
i entered in save mode and tried to change the resolution. a p200 was at high resolution 768×1024 but monitor was at 480×640(i have tested the monitor on a 486 and had marked this).
is the procedure the same when in windows resolution is lower then the monitor settings(higher)? maybe i do not understand between ok and enter/take over. pc and monitors are checked and ok. i had the same problems with 2 monitors. maybe. i have done these procedures very long time ago.