I want to sing better!! Help me!!?!

I want to sing better!! Help me!!?

I do kickboxing so I don't have time to go to a vocal coach so do any of you know how I can improve my singing voice. I'm aiming for a voice like Hayley from the rock group Paramore. I can hit the low and mellow notes but not the high ones. How can I improve my range and make my voice stronger? What are and what type of voice scales do I have to do? Thanks for the help!!!

There are certain warm ups I've done when i was in chorus in highscool. i don't know what note we started on, but we gradually went up an octave until our limits. It helps strengthen your range.

They are:

"Diction is done with the tip of the tongue and the teeth." you have to sing it to your self and try to put your own rythem to it.

"Sing we together all day long
now sing we all this joyful song
Now descending never ending
All day long." it sounds like a little nursury ryme, but it helped.