The front part is a bit tricky to change sprockets. I have a mountain bike with three sprockets, I also have difficulty with changing them. It all depends on the design of the changer. I am able to change from large sprocket all the way to the smaller but from the smaller sprocket to the second is okay but going into the third (large) sprocket is a real problem and no matter how hard an adjustment I've tried, it still doesn't want to go to the far end. Example, if it is in the smaller sprocket, it changes okay to the middle sprocket but it will not fully change in the larger sprocket because the cable doesn't fully push the changing bracket far enough to roll the chain on it. So, as with myself having same problem, I'd say, never buy a bicycle that doesn't change the front sprockets with ease. But while you have one of these three front sprocket bicycle, you have two options. Try and put the bicycle on a stand and adjust the changer's screws so that it can reach the far end where the large sprocket is, or in another case -where the smaller sprocket is, depending where your problem lies, the larger or the smaller sprocket). Remember that the air test is different to the road test. On the air test (bicycle on stand) the changer may be able to change sprockets but on the road the chain is heavily under tension and may not over-jump into the larger sprocket, but down-jumps into a mid or smaller sprocket quite easily. So, the best thing you can do is to not to apply force to the pedals to relieve the chain of any tension so that it can jump over the larger sprocket. But apply tension to the chain, such as 'accelerating', and it will not over-jump the larger sprocket with ease. However, if you change down to a smaller sprocket while 'accelerating', it usually changes without problems. The other option you can use is to sent the bicycle to a store and have it fixed there. Work is guaranteed and you can be sure your worries will be over.
Answers & Comments
The front part is a bit tricky to change sprockets. I have a mountain bike with three sprockets, I also have difficulty with changing them. It all depends on the design of the changer. I am able to change from large sprocket all the way to the smaller but from the smaller sprocket to the second is okay but going into the third (large) sprocket is a real problem and no matter how hard an adjustment I've tried, it still doesn't want to go to the far end. Example, if it is in the smaller sprocket, it changes okay to the middle sprocket but it will not fully change in the larger sprocket because the cable doesn't fully push the changing bracket far enough to roll the chain on it. So, as with myself having same problem, I'd say, never buy a bicycle that doesn't change the front sprockets with ease. But while you have one of these three front sprocket bicycle, you have two options. Try and put the bicycle on a stand and adjust the changer's screws so that it can reach the far end where the large sprocket is, or in another case -where the smaller sprocket is, depending where your problem lies, the larger or the smaller sprocket). Remember that the air test is different to the road test. On the air test (bicycle on stand) the changer may be able to change sprockets but on the road the chain is heavily under tension and may not over-jump into the larger sprocket, but down-jumps into a mid or smaller sprocket quite easily. So, the best thing you can do is to not to apply force to the pedals to relieve the chain of any tension so that it can jump over the larger sprocket. But apply tension to the chain, such as 'accelerating', and it will not over-jump the larger sprocket with ease. However, if you change down to a smaller sprocket while 'accelerating', it usually changes without problems. The other option you can use is to sent the bicycle to a store and have it fixed there. Work is guaranteed and you can be sure your worries will be over.