How can i expand and tone my range?

I can sing but my higher notes sound crackly and not on pitch. I need to know how to expand my range and hit the note perfectly without a problem. Also I can do vibrato on the higher notes but sometimes it doesn't come out quite so clear. How can I make it so I can get the vibrato everytime. One more thing.. I find my voice to be kind of monotone. Is that just because my range is too small for the song? Sorry about all the questions but I'm really thinking of giving up singing. Thats why I need to know if these are problems you can fix.