No need to do anything drastic, just make a few small changes. Its like I went back into W1609 and decided to modernise my fleet there. I had quite a few jets (Fokker 100's mainly) as well as ATR 72s and I ordered in a variety of E-Jets (195/175 and 170s) to replace them.
My maintenance went from 27mil to 60mil when my new E-Jets arrived (Age 0), but when I removed all the old aircraft from my fleet and had a larger fleet of E-Jets instead my maintenance dropped back down to 16mil.
So have a look and see what happens if you replace the 4 A330's and that 4 year old 777. It may or may not do good.