hp photosmart inks

[Candyred]

Hi, hope someone can help. I have a HP photosmart all in one c310 printer which holds 5 ink cartridges (3 colour, 1 small black and 1 XL black). When the small black one runs out how do I use the ink in the large black one. It seems it's just sitting there and not being used. I've tried the HP website but they just keep on about buying new cartridges but why do I need to when I have a full XL one. I just use it to print text now and again, it's eating the little cartridges and I don't get the amount of sheets that it says it will print :(

[treetops1]

Looking at this the other cartridge is for photos and cannot be used the same as a black cartridge. Hope I have got this right.
http://h20000.www2.hp...3238&prodTypeId=18972

[Candyred]

How do I get it to use the XL Cartridge though. I can't find the instruction as to what I have to do.

[treetops1]

http://h30434.www3.hp...artridges/td-p/226444