I purchased my c4600 printer about 4mths ago and i have just replaced the ink cartriges and it keeps telling me to realighn cartriges how do ido that it is the first time i have needed to change them i have not had any trouble with last hp printer

Here's a support article taken from the HP website regarding alignment of print cartridges. Hope this helps.
Introduction This document provides steps to align print cartridges using the All-in-One control panel or the computer. The appearance of the product varies by model. Aligning print cartridges Follow one of these methods to align print cartridges. NOTE: If the same print cartridge is removed and reinstalled, the product will not prompt to align the print cartridges. The product remembers the alignment values for that print cartridge, so there is no need to realign the print cartridges. Method one: Print an alignment page using the All-in-One control panel When a new cartridge is installed, the product aligns the cartridge. The cartridges can also be aligned any time after you install the software. Aligning the cartridges helps ensure high quality output. Follow the steps to align newly installed cartridges.

1. When prompted, make sure plain white letter or A4 paper is loaded in the input tray.
2. Press the button next to OK on the control panel display. The product prints an alignment page. Figure 1: Alignment page
3. Place the alignment page print-side down on the right front corner of the glass. Figure 2: Position the alignment page
4. Press the button next to OK on the control panel display. When the On button stops flashing, the alignment is complete. Remove the page and recycle or discard it.

1. Double-click the HP Digital Imaging MoI purchased my c4600 printer - c01367004.gifn ( ) on the lower right side of the Windows taskbar. The HP Solution Center displays.
2. In the HP Solution Center, click Settings . Then click Printer Toolbox . The printer Toolbox displays.
3. Click the Device Services tab.
4. Click Align the Print Cartridges .
5. When prompted, make sure plain white letter or A4 paper is loaded in the input tray.
6. Press the button next to OK on the control panel display. The product prints an alignment page.I purchased my c4600 printer - c01369744.gif 3: Printing an alignment page
7. Place the alignment page print-side down on the rightI purchased my c4600 printer - c01369745.gif of the glass. Figure 4: Positioning the alignment page
8. Press the button next to OK on the control panel display. When the On button stops flashing, the alignment is complete. Remove the page and recycle or discard it.