Are the brakes caliper or vee ? If caliper their will be a small allen screw to even up the arm movement, usually on the rear arm at the top, unless they are really cheap ones in which case you can only try to centre them on the locking bolt. Undo locking nut place a cone spanner on the spring spacer hold in centre do up locking nut. If they are a vee brake you should have a little screw on each arm wind out to move the pad in and in to move away do this on both sides a bit at a time until no rubbing, activate brake after each adjustment.