Daycore is a genre of digital music similar to Nightcore. Daycore is music that is changed to have more speed/tempo and reduced pitch.
Select a music file and open it with Audacity.
Then, go to "Effect" > "Change Pitch".
Lower the pitch percentage to a value between -25 and -10 (in the "Percent Change" box). The exact number depends on the pre-existing pitch and the listener's preferences/likes.
Test and change the value as needed until the music sounds great.
Next, go to "Effect" > "Change Tempo" and increase to tempo by 5 to 20 percent as needed/desired.
Again, test and change the value as needed until the music sounds great.
Lastly, save the music file by going to "File" > "Export".