Guitar Warping

I just bought a Haydn acoustic guitar, not sure if this mark exists by you and not really a top-notch one, but I liked it. It's the first I bought myself.

Every time after playing I loosen the strings instead of leaving it tuned afraid if I leave them tuned the guitar will warp. So that's my question: should I worry my guitar will warp if I leave it tuned?

The first guitar we had was terribly warped. The most recent one was left home by a girlfriend of my brother, and she left it home because it was practically unusable. But I bought strings and stuff 'coz I wanted to start learning something, but the strings were so high I couldn't play anything beyond the 5th fret, besides my fingertips had terrible calluses. So I don't wanna have my brand new guitar warped like the other ones.

Is leaving them strings tuned really a problem or does it depend necessarily apon other factors like wood quality or heat?

Thanks for any information, this forum is very good.

One detail I forgot: my guitar has steel strings. I know the steel strings exert more pressure apon the neck of the guitar, but they have a better sound, in my opinion. Or doesn't it make any difference if the strings are of steel or nylon?

Acoustic guitars have steel strings, unless you're playing a classical guitar.
In which case they're nylon.

On a decent guitar, you shouldn't have to worry about warping.
That kind of stuff usually only happens when you buy inexpensive, no-name guitars from department stores etc..
On a known brand, you should be able to leave it stringed up for the next 30 years and not have to worry about it.