Good Dumbbell training program required

I am male, 49. I have poor strength in my upper body. I am trying to do 100 pushups program. But I am finding it very difficult. After 7 days, I am still on Day-2 and cannot yet do it. I thought of using dumbbells to improve my upper arm strength.

I started with 3kg (6.5 lb) dumbbells. But the bicep curl and tripep curls seem not at all challenging. I know I have to increase the weights - but by how much?

Does any one of you know of and can recommend a good, internet based dumbbell training program on the lines of c25k/hundred pushups, etc?

Thanks