If I had to choose between cardio and weights, I'd go with the weights every time. Studies have shown that an challenging weight workout done circuit training style (one exercise right after the other with minimal rest) will burn MORE calories than an equivalent amount of cardio, keep your metabolism elevated for hours after the workout, and - like Mel posted - build muscle to raise your metabolism. All good things for weight loss.

Fortunately, we don't have to choose between cardio and weights. Both are an important part of any exercise program, as are flexibility, balance, and core strength training. It sounds like you're doing a ton of cardio already, so perhaps some more weight training (you said that you're doing some already) would really kick the fat-burning into high gear?

How many days per week are you lifting? Are you working out all your muscle groups? How many reps per set typically? Do you lift to failure? All these are variables that you might want to look at in order to increase the intensity of your workouts.

Well.....about those questions.
I do 12 reps 3 times on every machine that my gym has....on Monday, Wednesday, Friday and Saturday. But only on arms. My legs are bigger than normal since I pratice taekwondo (martial arts) for 10 years and I have alot of muscle there, so I don't need. Besides, after the muscle thing I run for 45 mins in a row, I guess that's enough for my legs.

Well...everything I'm saying I started doing it last week, yeah. Before that I only did cardio and everytime I tried to play with weight I couldn't hold 'cause I always tried to do it after the running thing.

I'm 1 meter and 84 centimeters tall.....dunno that in inches or feet. And I weight 87 kilograms. And yes, I'm overweight, it's not only water retaining.

Besides, my true question was "What's the way to remove the temporary water retention?"....any tips for natural diuretics? easy to get? I'm asking this 'cause I may look much fatter in a day I retain water.....and as I said, I can't wear my favorite jeans on those days, so in order to prevent it I must know some way to remove the water.

Don't mess with diuretics unless you are under the supervision of a doctor. It could cause all sorts of short-term and long term health problems up to and including a heart attack...even at 21 years old! No matter how "natural", they still deplete your body of water, causing chemical imbalances.

The only safe way that I know to retain less water is to lower the amount of sodium from salt and carbohydrates that you consume. Again, start with eliminating the simple sugars from your diet. Then it's back to basics: nutrition, strength training, and cardio. Ditto what Meg said: try to increase the intensity of your workouts by increasing your strength training intensity. Don't just train arms...you have a back, chest, shoulders, core, and legs. Even doing a lot of martial arts is not the same as weight training. The more muscle you have, the more fat you'll burn. Give it some time. A week isn't enough to tell if its working. Try 8-12 weeks Do your weights before your running or on alternate days.

Mel

Moonsoft -- I agree with Meg and Mel 100%... One thing that wasn't mentionned is your water intake.... Do you drink 2-4 litres of water per day? This helps eliminate excess bloatness...

I reduced my carbohydrates and used some natural diuretics, that is onion, garlic and coffe (without caffeine) and some tea. And it worked pretty well on removing this temporary faking fat. ^.^