Try using a hair dryer to soften up the glue. Use something to 'pry' the pieces up since they'll be REAL hot.
After that, you can forget about painting your bathtub. 1) It won't last. 2) You didn't say what it is made of. You may want to look into either reglazing it or having an insert installed.
My best to ya and hope this helps.
Jay J -Moderator
PS: God Bless America!