really simple - if you are in the shower take the shower head off the wall and hold it above your head yourself - discovered this in a rented flat once - the shower fell off the wall and the landlords took 2 months to fix it - in the mean time my arms had never been so toned!!
Hold a tin of, say, beans, in your hand. Raise it straight up, in line with your shoulder, past your ear. Bend your elbow so it points forwards and your hand (and tin) go down towards (and past if you can) your shoulder, sort of backwards. You'll feel a pull in your tricep. Do it as often as you can. If you want to you can use weights to do it but be careful they aren't too heavy to start with. Also be very careful of your back position, you can sit on a chair.
Another one is dips - sit on the floor at the foot of the stairs with your back to the bottom stair . Place your hands palms down, fingers forward on the bottom stair. Lift yourself up and down with your arms.
Google Tricep exercises as you will be able to find loads.
Building muscle in these areas will only give it shape once you loose the fat from it, you cannot spot fat and by that I mean you can't choose where to target fat loss.
You need a correct diet and exercise plan and bit my bit the body will burn the fat stored and you will see a difference.
I've found that sweeping the yard worked wonders for my arms - made everyone else happy as well lol.
Also, stand with your back to the side of the bath, place your hands on the edge of the bath (either side of your body, slightly wide). Bend your knees so your arms take your body weight. Dip up and down - slowly and controlled. Do about five times and build up the repetitions over time.