I agree with Phil: you should spend some time with someone who can guide you properly, such as a pronunciation teacher.  Shadowing is still a good option, but you also need to learn the sounds in the new language, even if it means learning the alphabet again.

One problem I've often encountered with my own language learning is that I wasn't saying what I thought I was saying.  I was following English pronunciation (and not, say, Italian pronunciation), or misunderstanding how certain pronunciation rules work (such as vowel reduction in Russian)  or I honestly didn't know how to make the sound in the first place.  I needed someone to tell me what I was saying wrong, and then show me how to do it right.

As for your accent, treat it as a continually-developing thing. A person's accent will change through life, depending on where they go, who they speak with, and so on.   You can train yourself towards certain accents, just as actors do, but remember to be open to influences.

Firstly i want to say that as long as you can be understood, then your accent is a beautiful thing, and it isn't necessary for you to lose it.

However, if you feel your accent is too strong I absolutely recommend shadowing to help you.

Here's a great video about how to do it from a Korean language teacher friend of mine.

https://youtu.be/CwGkaRFHOlE

and here's an article that he wrote that goes into more depth

https://medium.com/@mindlightgrow/if-you-re-a-language-learner-you-better-be-shadowing-1aca99c061e7#.6v2jfge0p

Good luck!

Try recording your voice saying something and then listen to a recording of a native English-speaker saying the same thing.  Then practice and record each word or phrase until you notice an improvement.  

Pick ONE English accent to copy.  Do not mix accents because you may become difficult to understand for everyone.  

There may be some words that you will never be able to say, and this is okay. Accents are cool!