Order I would use, since you asked: clean everything, then switch to a fresh medium roast, then filtered water, then adjust steep time and grind. Change one thing at a time or you will fix it and never know what it was.
Steeping too long is lower down the list because over-extraction usually reads as harsh and bitter rather than ashy specifically, although it will make an already dark roast worse. Slightly coarser grind and a shorter steep within your recipe's range if the first four do not do it.