I hope I understood your question correctly.: You want to delete your old Spotify account and add the new one to your computer. Lastly you want your iTunes songs on spotify.
Firstly to delete your previous spotify account, go here and then click on account>close account permanently.
Then open the spotify desktop app. Click on your name and go to settings. from there scroll down until you see this:Go to local files, check all three switches there.
Then go to local files and there you can see your whole iTunes library. If you liked my post: Feed my ego with likes :-D If this post has solved your issue: Please accept this as Solution Music is a world within itself, it is a language we all understand. ~ Stevie Wonder