To change to sound effects. Use wav to change. So pick yur recommending audios for ideas to change. Got to cloud convert. Put your audio. If its a mp3. Put the format: mp3 to wav. Put your same audio and convert. To change the ost. Its a ogg. Put your ost that you like. So download it. So go to cloudconvert again. Change the format to mp4 to ogg. Put the same downloaded ost and convert. Go to z archiver. So go to downloads. And find the same ost and sound effects. Put the wav on the changeable assets. Go to audios. And put the 2 sound effects. Delete the 2 sound effects. (not the files that you did.) And rename them to the same file names of Music.ogg and MainMenu.wav And BOOM! done! (typed it for a minute hope this helped)