There are hundreds of short listening activities with transcripts and questions to answer here: elllo index Click on the word "Level" in the left column and you can search for activities based on the level, the topic or the nationality of the speaker.
Don't worry too much about having an accent. We all have them, it is part of who we are. If you do want to change it though, find an accent you like and practice it. Take a speaker from ELLLO or someone from a video on youtube and try and copy exactly what they say. It's easy to record yourself on a smart phone or using free software like Audacity or a website like Vocaroo | Online voice recorder. Compare your recording to the original, try to isolate the differences and record it again!