You need 3.0 and up to be able to choose from early startup, sry.
where pressing a key (or at least space) on the early startup screen will toggle between pal/ntsc. I can't remember if there was a radio button as well, but someone at commodore obviously thought there was a big problem that someone would have a monitor that didn't support the default region your amiga was set to.
I haven't used 2.04 for ages, so I can't remember if there was a hidden option like that. However there are CLI programs and bootblocks that allow you to switch.
Or you could use screenmode to change it, as long as you have PAL and NTSC monitor drivers installed it should work.
Depends on why you want to switch. Being in a PAL country all mine are set to PAL anyway and I have rarely had a need to switch to NTSC.
