Deciding that you need to lose a bit (or a lot) of weight is easy. Following through is the tough part!

So how to motivate yourself?

A good idea is to write down how you think you'll feel if you succeed in losing however many pounds you want to lose.
Will you feel more energetic?
More confidant?
Happier?
Healthier?
Will people be happier to spend time with you?
Will it be good for your love life?

Whatever it is that you yourself feel will be the results of losing weight, write it in a list and put the list on your fridge.
Then add a 'before' and 'after'picture of you when you were slim and you as you are right now.
Then every time you go to the fridge, look at the pictures and read one of the items on your list.

Now start another list (for the fridge of course) with what you are going to eat to transform yourself back to your slimmer self.
Maybe decide that for one month you will eat nothing but raw foods and that at the end of a month you are going to evaluate whether this has made you closer to the way you want to be.
If that is the route you are taking, then fill the fridge with cantalopes, celery, carrots, watermelon, lettuce, cucumbers, spring onions, tomatoes, all sorts of berries, apples, raw nuts and seed etc. Make sure that there is plenty of all your favourite fruits and veggies and nuts and seeds.
Make yourself fresh juice at least once a day, maybe fresh carrot and celery juice with a little garlic and basil once a day, and an apple juiced with nuts and blueberries at another time.

Whatever you do, don't go hungry. Eat until you are full! Depriving yourself that way is a sure route to failure.