If you find your bike isn't feeling very comfortable, you may only need to make a few small adjustments to your seat (saddle) or handbars.
Saddles should be set with their tops level, or parallel to the ground. Tilting the saddle's nose up is uncomfortable. Tilting the saddle's nose down will cause you to drift forward onto the handlebars. Pushing against the bars might make your shoulders tense up.
To determine correct height, sit on the saddle with both heels on the pedals, and pedal backwards slowly. The saddle is at the correct height when each leg straightens fully as the pedal passes the bottom. Your hips should remain level on the saddle. If they roll, the saddle is too high and your legs may over-extend, which can damage your knee joints. If your knee is bent when the pedal passes the bottom, the saddle is likely too low. Some new riders may prefer a slightly lower saddle height, so they can reach the ground more easily. This is better for your knees than having your saddle too high.
Setting the saddle height with your heels on the pedals, ensures your knees will have a slight bend when you put the balls of your feet on the pedals. This keeps knee joints stable and protected.
Bring the cranks parallel to the ground, then place the ball of your foot on the front pedal. If the saddle is in the correct position, a line drawn from behind your kneecap would fall through the pedal's axle.
Ride with the new position for at least a couple of weeks before making any changes, and then only make small changes (not more than 5mm at a time).
Correct height allows you to lean forward comfortably, without straining your back, neck, or wrists. Depending on the type of bike your ride, and your flexibility, you may want to adapt these guidelines slightly. If you're not particularly flexible, you may prefer a higher or shorter handlebar stem, to bring the bars in closer and allow you to sit more upright.
Urban: 2.5cm. above to 2.5cm. below the level of the top of the saddle.
Mountain: 5cm. to 10cm. below the top of the saddle.
Touring: 2.5cm to 5cm below the top of the saddle.
Sport: 5cm to 10cm below the top of the saddle.
You can change the angle of your handlebars by loosening the handlebar clamp on the stem and rotating the bars. Try out all the hand positions you'll use when you ride to make sure the angle is comfortable. Remember to tighten the clamp when you're through.
Your stem sits on a stack of spacers, and is clamped to the steering column by two 5mm Allen bolts. An adjusting cap sits on the top of the column, and is anchored by another 5mm bolt. You can change the height, by removing some spacers, but be aware that doing so may change the headset adjustment (the bearings in which the fork turns). To make sure it isn't too loose or too tight, it might be best to have this adjustment done at a bike shop.