If your shares has become more valuable than when you bought them, you can realize your profit by either selling your shares or receiving dividends from the company.
The most common way to realize a profit is if the company is bought by another company. Potential buyers include industrial companies such as pharma companies and financial companies such as venture capitalists. You can also sell your shares if the company lists its shares on an exchange. It is more difficult for an individual investor to sell its shares if they are not listed on an exchange but you are generally free to sell them if you find a buyer.
Investors can also realize profits by receiving dividends from the company. As an investor in early-stage companies, it is important to note that such companies rarely pay dividends since they need their money for growth.