Who's wall is it?

Picture would help.

You have to have access. Is there access across another property?

This will cost a lot of money.

Are you talking about 75 LF of jersey barriers that are backfilled and currently supporting a deck? Sounds real expensive to remove, dispose of, and replace with a new wall.

As others have said, a big bucks project. You'll need an engineer to design a solution that will keep everything standing up while you work on it and generate stamped drawings assuming your jurisdiction requires them (mine would), someone with a crane to lift out the jersey barriers, and probably more crane time to get your new wall materials in place. Probably a good excavation contractor to demo the existing wall and prep for the new one and a mason to build the new one. Landscaping firms that manage large projects should have the necessary resources and be able to do this. I'll bet you're looking at $50K at least, depending on the material you'd like to end up with. If it's working to hold the ground in place I'd be seriously tempted to plant an aggressive vine to cover it up and forget about it.

Where's the need to remove the wall? Why not just build a properly engineered wall in front of and over the existing?

Here are a couple links that may assist you in the removal;

http://www.thebluebook.com/

The search term is traffic barriers.

http://www.bpmselect.com/?id=2&region=7&bkid=7&keyword=Concrete+Traffic+Barriers

You said the previous neighbors put the wall in. What has that got to do with you? It's the guy that is there now that has the problem, not you? Only way it might be partly your problem is if it is on the line then it could be argued you are both responsible. You say it is leaning towards the neighbors, so he has a big problem not you.

Thanks for the informative post. I bet I have a better idea now on how to handle retaining walls that are built in bad condition and directions.

Here is a link that might be useful: Downers Grove Fence Company