The general idea is that nipple stimulation releases hormones and these cause breast enlargement. HOWEVER, the stimulation needed to get hormone release is fairly rough, pinching and pulling and most women find it uncomfortable to painful. You can try but be sure to use a oil lubricant or your nipples will hurt more than you realize at the time and only later will they complain bitterly.
Also be aware that nipple stimulation can obviously cause sexual arousal - this causes breast engorgement in as many as 50% of women and it can lead to up to a cup size in increase - but it is only temporary.
Other more sure methods are waiting til you get pregnant - gains of up to 4 cup sizes are common - although not forever. Also going on the pill causes significant breast size increases in many women