Hello all.
About five years ago I signed with a reputable literary agent for a manuscript. He sent it out but ultimately there were no takers in the great world of New York publishing. It was disappointing, but I see now that it was for the best. He asked me if I wanted to revise and I decided I was going to put that away and work on something else.
I'm nearing completion on my new project and realized a long time ago that I need new representation this time around. My former agent is well respected and was professional with me, but I was very young and green, to be honest, signed with them because they were the only ones who offered at that time. We weren't a good match for many reasons and every instinct in me says that we aren't a good fit and I need someone else. I'm not the same person or writer. My mind is made up on that front.

My issue is that I haven't heard or spoken to this person in almost six years and I don't know quite how to approach this. I don't want to "break up" by e-mail or a registered letter, because all the websites say that's unprofessional, but at the same time this person hasn't reached out to me in all this time (ditto on my end) so it seems like it would be really really awkward to just call and say "this isn't working, all the best". I also know that NYC agents talk, and I don't want to hurt my chances with other agents who might think I'm being a flake and not to be trusted. Trust me, I've come to this decision after years of thought.

If I call, I feel like the agent might try to convince me we could work on it, but I'm definitely not going to stay his client. There's nothing to be gained from laying out the issues I have because they aren't small details but big picture things. At the same time, when I'm querying for the new manuscript I want to be upfront and say I was represented before, but I wonder how many agents would think twice about working with me if they knew I up and fired an agent without at least trying to work it out.

I would be really grateful for any advice on how to approach this.