Consider going to vocational programs that offer free evaluations for skills. Also, local community colleges may be able to assist you. The local school board office may have some connections and local libraries often have information for adult learning opportunities.
I'm glad to see your interest in learning - it is very important that you are motivated. Having the intention to learn and maintaining the interest will help you a lot in achieving your goal. One thing that will help is to set aside time in your schedule to read about subjects that interest you, for example, science. Reading more will make you better at reading. Reflect on what you read and keep a journal of ideas you like. You can also learn from videos or other media. I would recommend subscribing to a magazine about current events, like Newsweek or Time, or even a daily newspaper (if there is one where you live). Smithsonian is an inexpensive high quality magazine with lots of information on history and science. There are a lot of good videos on YouTube explaining things. Also the Kahn Academy is a great source of learning more. Good luck!