If you are aiming for a 10k race then there is no real benefit for running for longer than 1hr to 1hr 30min, depending on your speed.
Instead try doing sone of your runs faster. Remember, calories burnt equates to distance travelled and effort put in rather than time, so you can burn more calories on a short fast run than on some long slow runs.
But don't forget to have some slower runs too. Your body can't sustain doing every run fast, or every run long.
I would aim to do something like this:
Mon: Slow, short recovery run. Maybe 30 min. The aim is to get the circulation going but not to push yourself as you will be tired from the long run at the weekend.
Wed: Speed work or hills for between 30 min to 1 hour. This will improve your speed and stamina but without over working your legs
Sat: Long run of 1hr to 1hr 30 min. Slow and steady so that you can maintain the same pace all the way round. You can do the occassional hill, but the idea of this is to build stamina for the race.