As lindy loo says check your deeds. They will tell if the fence is yours and also if you are responsible for maintaining them, frequently there is no legal responsibility to maintain them.
Have a surveyor come out and find your surveyor stakes. Then look to see whose property line side it is on. I had to do that. Found out it was on there side 3 inches onto there property line. Not my problem.
If the fence is yours then you must maintain it. Also check to see if your neighborhood has a community association. They have guidelines as to what is your responsibility involving fences. Sometimes they have limits on height if putting a fence in. So please check.