How to vary the duty cycle of PWM with ATMega328

[hector1]

Hi everybody this is my first post and I need help on a program that I´m working on. I'm using the ATMega328 and there will be 6 push buttons connected to it,with the buttons you will select the speed of a motor for PWM, the firts button will turn on a motor like a 17% for PWM, the second at 34% .....and you get the idea.
The problem is that i don't know how to change the duty cycle of the PWM:-|.
I'm doing the program step by step and I have accomplished to turn on the motor at 100% but i can´t vary the duty cycle of the PWM.
This is my program I hope you can help me ;-)

	.include "m328pdef.inc"
	.def stack=r16
	.def temp=r17
	.equ increase=5

; configure stack
			ldi stack,low(ramend)
			out spl,stack
			ldi stack,high(ramend)
			out sph,stack
;define I/O
			ldi temp,0x00
			out DDRC,temp
			com temp
			out PORTC,temp
			out DDRB,temp

			ldi temp,0x81
			sts TCCR1A,temp
			ldi temp,0x09
			sts TCCR1B,temp

	;begin the comparator with 00	
			ldi temp,0x00
			sts OCR1Ah,temp 
			sts OCR1Al,temp

			lds r20,OCR1Al
			ldi r21,increase    
continue_up:      add r20,r21
			cpi r20,0xff
			breq wait
			
			ldi temp,0x0
			sts OCR1Ah,temp
			sts OCR1Al,r20
			jmp continue_up
wait:    	        jmp wait

delay:     	        ldi r23,0x5
another:	   	dec r23
			brne another
			ret