Quake3World

how to change point of view to another player in recordewd demo?

Short answer: you can't.
Long answer: There are mods that support recording demos that allow this, like Ultra Freeze Tag and perhaps OSP (but I'm not sure about the latter), but without such a mod, it is not possible.

There are a few limitations to it, but you can use Q3MME for this.

It is more focused onto movie making (not demo viewing as such) so I'm not sure if it is what you're looking for.
Most of the features are explained in the "tutorials" section.

With ChaseCam you can lock on all kinds of entities: players, weapons, projectiles (rockets, grenades), ammo, health and armour.
I'm not sure if it's possible to get the exact POV of a player when he played the game...

More info for perhaps some other ideas (I'm not familiar with these).

Its still limited to your own PVS (potential visibility set). Because your computer only knows what happends within the area you can see (that is a really simplified way of saying it) it won't record movements of players outside of that area. So unless Q3mme has its own demo recording facilities for this its still limited.

edit:
should've read the thread you linked, it explains about server side demo recording right there...

the mod CPMA records multipov demos, so you can watch 8 diferent povs in a team game, watch 4 at once, or "picture in picture" style for duel. This is also available on gtv and when you are "coaching" a team.