Renegotiating My Hourly Rate

[juancano1967]

I started freelancing at the beginning of 2021 with no paid experience outside of informal departmental editing for my primary job. I had no idea what to charge for my proofreading and editing services, so I took UpWork's default hourly rate.  A year ago, I landed a long-term contract with a great client and still do consistent weekly work with him (up to 20 hours).

A year later, I'm currently charging about 25 - 40% below national averages to my client. Because of this contract, and a little job creep into other areas that a higher-level editor would normally handle, I have gained much more professional experience.

How do I go about asking for a raise when we have a set contract? I don't want to lose the contract for being greedy, but I feel the quality of my work has greatly improved and I should be compensated accordingly. Also, UpWork doesn't allow me to raise my rate on an existing contract, just lower it, so I have no idea how the details work.