You can
only charge a LiPo or LiFe battery at the nominal voltage, stated on the battery itself.
So if you have a 2s/7.4V pack, as you do, the
only voltage it can be charged at is the 7.4V (2s) setting.
Same goes for 3s/11.1V, 4s/14.8V, etc. I'm sure you get the idea.
You can alter the charging current, in Amps, but there really is no benefit, apart from the time it takes to complete the charge. It certainly is not like older NiMh or similar, where a higher charge current might allow for better performance, with LiPo/LiFe the general rule is to never charge at anything above 1C. I say general rule, as I have a recent Turnigy pack which is perfectly ok to be charged at up to 5C, which would probably start a fire with most other 'normal' LiPo packs.
Don't forget to plug in the balance cable in the 2 cell balancing port on your charger. Charge your pack often as you want and never let it get much lower than 30% capacity as it can damage the cells. Best to charge as often as you like because LiPo/LiFe batteries will actually last longer and give more stable performance if charged often and not allowed to go flat or <30% capacity. Google LiPo battery technology or charging or go to MaxAmps.com or some other battery manufacturer's site and you will find a wealth of info about how to make best use of your LiPo's, how to not ruin them, etc.