I purchased some songs from another account, and now i want to change my account but I need to wait 75 days (they were 90 days) so I can use the other account in my device. I cannot wait, what can I do?

A 90 day association only starts when you redownload past purchases, use iTunes Match or use automatic downloads : iTunes Store: Associating a device or computer to your Apple ID. If you can't wait until the 90 days have completed then you can try contacting iTunes Support and ask them if they can remove the association : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page. If they do and you log into a different account and redownload the songs then you are likely to start a 90 day association with that account instead.