Wait until the seed pods are ripe, brittle and beginning to split of their own accord, then plant the seeds in seedling compost, say three or four to a small pot, keep them watered and put them somewhere sheltered e.g. a cold frame or unheated greenhouse ( I manage without either) and shaded and they should produce small seedlings. When they have developed a few leaves, pot them up singly into multi-purpose compost and when they are big enough to put into the garden, next spring, say, plant them where you want them to grow. However, you should be aware that they may not come true to the same colour as the parent plant. I don 't entirely understand why this should be. Good luck.

Most garden Lupines are complex hybrids of several different species and color forms. Therefore, when they form seed, the genes re-assort, and the brown-haired, brown-eyed parents come up with a blue-eyed, red-headed kid! Sometimes, especially if you have to store the seed for more than a few days, you may have to gently file a hole in the seed coat to allow it to sprout before next year.