i can tune my guitar up to 100% but when i play the string one octave higher (i mean first 0 and then 12) the 12 always is out of tune, what can i do to make it in tune?

Intonate it. Its hard to explain if you dont really know youre doing. What kind of guitar is it?
it's a silvertone (the kiss model ( i don't know what type haha sorry) )

but how to i intonate it?
Honestly the best, and easiest way to fix it-as well as any other problem that youre unsure of-is to take it to a professional. I good set-up (intonation, string height, and truss rod) costs only about 50-75 US dollars. And that way your axe will play and feel perfect!

But if youre a true do-it-yourselfer then Google "intonating guitars" or something along those lines and you'll get the best info that way.
Well for some reason, I have a 24 fret neck, the 12th fret harmonic and fret are in tune, but the 24th isnt!
I'd take it to a pro....I was gonna buy that guitar, it's called the Sovereign Special, or the Sovereign Pro, depending on how much it cost the pro is better, but theyre both alright...they look nice anyway.
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