[hugo31370]

My first advice is, you should get a lawyer to do that (I'm not a lawyer).

If you're a C-corp, ideally you haven't issued all stocks you're authorized to. Usually you're authorized to issue 10M stocks and you then limit the number of shares outstanding. If that's the case (say you have less than 5 million shares), you can just make your co-founder sign a stock purchase agreement on the # of shares you want to give her/him.

If that's not the case and you own all 10M shares, the company will have to buy back shares and then transfer them to your co-founder (via stock purchase agreement). The downside is that the company will have to pay for those shares (usually we're talking about a few hundred dollars).