Gear ratio effect on stopping/skidding

i got a front brake.
but im using my foot to slow the back one so im shredding up my shoes.
it's 48/15.
whats best to get it changed to?
and do you change the chainring or the bottom bracket?

i feel that maybe you should have brought a grey hybrid instead of a fuji track.

1. buy a brake
   
2. buy a new rear spocket (19tooth if you want to skid lots and not go fast, or 18tooth if you want to go a bit faster).
   
3. leave chain ring and bottom bracket alone.
   
4. get a bike shop to change your spocket as you really don't have a clue - they'll do it for a fiver.
   
5. buy a brake