How many tracks are there? In what environment did you record this?
That hiss is pretty pronounced and I'm not sure that it can be mastered out without affecting either the vocals or the guitar, depending on which track it is on.
There's also a lot of reverb on the vocals. Is that room noise or was that intentional in the original recording? Was that reverb perhaps put on after recording? Was there some kind of filter placed on the vocal track? It sounds almost as if a high-pass filter was placed on it.
Depending on your answers to these questions will determine if the levels can be mastered to improve the quality.