The error message you received may not be about memory at all.
Does the fax refuse to send? if so you may have a problem on your phone line.
In which case... well, please tell me what your phone line service type is, so that I can advise you accurately and according to your actual phone line type.
As for ordering a printhead cleaning cycle:
on the printer, press the INK button, or the INK MAINTENANCE button.
Press the UP OR DOWN ARROW key to choose Test Print and
Press the UP OR DOWN ARROW key to choose Print Quality and
Press Color (Colour) Start. The Print Quality Check page should print.
Then, look at the four colors of blocks you will see on the page. The four colors of ink in the printer.
The printer will ask you, whether the print quality is OK for black?
Then it will ask about the other colors after that.
Then after that, it will ask about whether to
Start Cleaning ? Yes/No.
Press up arrow, or 1, or +, to select YES and the printhead cleaning will start and run for a few minutes.
Then press COLOR START, and another print quality page will print. Compare the two.