Hey all, I’m super new to Audacity. Like I just started an hour ago. I want to take a song I’ve downloaded and change the Hz to make it extremely high pitched. The end goal is to have a song that you can listen to, but it has an extremely high frequency similar to those mosquito ringtones that you can find online. I have no idea if this is even possible, like I said I’m extremely new to the program. Any tips would be appreciated. Thank you!
-Z
Try these effects:
http://manual.audacityteam.org/o/man/change_speed.html
http://manual.audacityteam.org/o/man/change_pitch.html
http://manual.audacityteam.org/o/man/sliding_time_scale_pitch_shift.html
Note that there is a limit to how high it will go before it becomes utterly destroyed 
Resampling to a higher sample rate will make processing slower, but should preserve the sound better when making your extreme changes. Try resampling to 96000 Hz before applying the above effects.
http://manual.audacityteam.org/o/man/tracks_menu.html#resample
(the resampling step is not generally required for “normal” use of these effects).
You might also try playing around with the high-pass filter effect. (A high-pass filter lets the high frequencies through, while blocking the lower frequencies.) Try starting at about 5000Hz, with a slope of 24dB per octave or more. That will leave you with just the higher frequencies.
The thing is, you’ll have to pitch-shift by a LOT to bring the bass up to a very-high frequency. And then, everything else will be shifted above the audible range and all you’ll hear is the pitch-shifted bass. So, filtering-out the bass (and maybe the midrange) may give you a better result.
You can try filtering before or after pitch-shifting. Or, high-pass filtering alone may give you the effect you want… You’ll just have to experiment…
You may need to use the Amplify effect when after you’re done with all of this, especially if you high-pass filter. Most of the energy is in the lower frequencies so extreme high-pass filtering will lower the volume by a lot.
There’s one thing to be cautious about if you are using a “high power” stereo system… You could fry a tweeter with sounds that don’t seem that loud or with sounds that you can’t even hear! For example, a “100 Watt” speaker is designed for music (or other program material) that hits 100W on the peaks for brief moments, with most of that power going to the woofer and midrange. The tweeter in a 100W speaker might burn-out with a 10W high-frequency continuous test tone. (This won’t be a problem with a phone or with “regular” computer speakers because the amplifiers don’t have enough power to do any damage.)