It's a common problem so don't be too upset by it.
If you ever have the opportunity to live among native speakers you will find it much easier to reduce your accent a bit. It is very difficult otherwise.
Can you ask your teacher which specific sounds are causing you the most problems and ask for exercises to work on those? Do you listen to any native English radio or language tapes and try to copy their pronounciations?
When I find it difficult to understand someone it often isn't their accent so much as the rhythms and stresses of their speech being too different to what I am used to. Again, you could ask your teacher for extra help in these areas.