Nasally? Like Bob Dylan? He took singing lessons and the result was even MORE nasal. But he has a million-dollar voice. Maybe you just need to find the right songs.
Ever scuba dive? Snorkel? Learn to breathe through the snorkel or mouthpiece underwater, without closing your nose or wearing a mask. That can help teach you how to divert air away from your sinuses.
Also: breathe properly. Inhale - your stomach should go out. Exhale and it goes in. When you sing, use your diaphragm to push the air forward, not your lungs.
Don't know if this applies, but in choir we were taught to emphasize the vowels, like for the word "glory" you'd sing it as "glow-ree" (like "glow little glow worm") instead of "glore-ee" (like story).