I'm trying to lose weight and I want to know the best ways to increase my cardio? I try to push my self to at least run or use the bicycle for 30 or 40 min but if I'm on the treadmill I can sprint maybe like 3 times and hold it for 3 min and the rest of the time I end up mostly walking (or speed walking). With the bicycle it can do a little better but not much?
To lose weight, your diet will be the most important thing you need to work on. As for cardio, I think that bicycle is an excellent way to start, since it is (in my opinion) better for your legs(if you feel you are overweight). I rarely do treadmill myself because of my knee.
If you feel like you have some cardiovascular endurance then you can try HIIT(High intense interval training). It can shorten your training sessions A LOT.
Basically what you do(i prefer on a bicycle or rowing machine) is use whatever you like and for, lets say 30 sec you work as hard as possible, then rest for 30 sec and do it again. Repeat this process as much as you like, you can start 6-7 times and move up to 10+. Later on you can play with the work and rest times. Like work 30 sec, rest 20 etc.
I found this being much more...fun than just cycling or rowing for an hour.
s3v3ns answer pretty much covers it, but I'd like to be more specific about the diet.
Doing cardio, even every day, will not guarantee that you lose weight (= have negative calorie balance), eating 500 kcal is much, much easier than running 500 kcal.
So I'd recommend that you write down what you eat during a week, and don't try to eat healther than normal, just write it down. In the end of the week, calculate the calorie intake you've had, and you'll see what adjustments you should make.