In Nigeria, our act allows for two major types of registration if your intention is to setup an NGO,
1) company ltd by guarantee and
2) incorporated trustees. I wouldn't venture into there merits and demerits which lies outside the scope of this question.
Another issue lurking underneath this question is, 'whether you can convert from a limited liability company to a company ltd by guarantee or an incorporated company? .our act is silent on this, it only allows for 5 types of conversion which these conversions are alien to. therefore its a total No, which invariably implies that you have to incorporate another company, but there is a little suggestion to help you retain the company's name as at when you decide to register any of the two above mentioned companies. You apply to change the name of the already registered/established LLC and when the change is confirmed, you will be able to register a new company with the already established name.