the best way is to manully edit the config file

goto /usr/etc/X11/XF86Config-4

edit that file, you need to scroll down tell you hit the display

you will see somthing like

"1280x1024" "1024x768" "800x600"

just put in the rez you want to be at before all the other rez's like for 1024

just change "1280x1024" "1024x768" "800x600"
to

"1024x768" "800x600"


you can also reset x without restarting by hiting ctrl+alt+backspace
that will kill x and then if you have auto login into graphic mode it will restart x for you.

but id edit the xf86config file. if your not sure how to edit it, copy and paste the text from that file in this forum and we can help edit it for you