hey ive recently started lifting dumbbells,im a girl, and i know they say that girls dont bulk up that easily...but so far my arms seem to be getting bigger, but i don;'t want it BIG, i just want it to look DEFINED. and at the same time i wanna build up strength...so wat should i do?should i use less weights and more repetitions or more weights with less repetition?

How much fat do you have on your arms? Getting definition is a mix of gaining muscle and losing fat, if you just gain muscle but don't lose any fat then you will mostly just look "bigger", alternatively if you just lose fat but don't gain muscle you will probably just end up looking the same but smaller. If you just recently started lifting then a little surge in muscle size is normal, it seems when your new to weights you put on more muscle in the first month then you do in the next year... Also as a woman your muscles are still able to grow, but their growth potential is SEVERELY limited compared to a man. No matter how you train, chances are your arms will never be "big", athletic sure, but not "big".

But we need more information.
How long have you been lifting?
What does your routine look like?
What is your current body like, and what are you looking to change?
Whats your diet like?

Take the guesswork out of your results tracking. Get a soft tape and measure your arms (as well as your hips, thighs, and waist). You then have to examine how measurements relate to the appearance you're aiming for, but whether your arms are truly getting bigger or not shouldn't be in question.

As body fat decreases, muscles can look bigger even though body part circumferences measure smaller.

An equivalent weight of muscle takes up less room than fat, so if you haven't gained weight, it's unusual that your arms would be getting bigger. Has your body weight changed? What does your diet look like?

For a defined look, your goal would be to reduce bodyfat percentage. That means to lose fat mass relative to lean body mass. Lifting with dumbbells is the part that increases or maintains your muscle mass. For maximum effect, this should be combined with cardiovascular activity and/or a calorie deficit to reduce fat mass.

To some degree, we can control what happens to our muscles by altering the load. In other words, manipulating the number of reps, sets, and rest time.

Here are a couple of an articles that explain it:
http://www.workoutamerica.com/opinion/article/reps/
http://www.bodybuilding.com/fun/dorian5.htm

Usually, people who are training for more definition like to follow a program similar to what's suggested for hypertrophy (8-15 reps, 65-80% of our maximum 1 rep max, and about 1 minute of rest between sets).