Usually you will have to apply for the renewal of the self-employment visa at the competent aliens' registration office. Their officials, together with the local IHK, will examine the financial situation, other aspects and your business plan, then decide whether you will be granted a visa renewal. If you wish to sell your company and establish a new business, it will affect your visa for sure, but how much and how you deal with it will depend on the decision of the local aliens' registration office, the negotiation with them and your new business.
