How can I clean the printheads on my HP DeskJet 2135 to fix print quality errors?

To clean the printheads, access the printer's settings through the HP software installed on your computer, or directly from the printer's control panel (if applicable). Look for a 'Clean Printheads' or 'Maintenance' option. The printer will go through a cleaning cycle, which can take a few minutes. Repeat the cleaning cycle if print quality doesn't improve after the first attempt. It is advisable to do this a maximum of 2-3 times, before seeking further assistance.