pruning tangerine tree, older tree

[jepitts4]

I have an older tangerine tree that I think needs to be pruned. This tree is about 12 feet tall and it is difficult to get to the fruit at the top of the tree. I have never pruned this tree and have lived in my home for 7 years. I have no idea how old it is. The fruit is very good and I do not want to harm it for next year. Also it is very dense and hard to get into the inner part of the tree to harvest. Thanks.