Anybody can edit Wikipedia. That includes you. So when you see a mistake, you can correct it. All you need to do is hit the 'edit' link at the top of the page, and make the edit.
Of course, that also means those with ill-intent can make changes too. And there is a lot of spam. However, there are enough users of Wikipedia that spam tends to last extremely short lengths of time.
There is also information added by people with good intent, but who aren't as knowledgeable about an area as they think they are. But, fortunately, more and more people are learning 'to light a candle, rather than curse the darkness.' That is, to fix it, rather than attack it. And contrary to another popular aphorism, the more cooks there are, the better the broth. (Especially if the professional cooks overcome any distaste of associating with the amateur cooks, and offer their expertise.)
Tips/Advice from someone who has edited Wikipedia entries.
1) Register and create a username. Your username doesn't have to be your real name. Some people use their real name because it sounds more professional, but it's not necessary, and people really won't think less of you if your pseudonym is DNAfreak (Some might think you're a fan of the late author, Douglas N. Adams though.)
You don't have to register. You can edit a page anonymously. (Your IP address will be recorded, so it's not really anonymously, but the IP address won't be traced unless you start posting libelious statements or something.) If all you are going to do is correct grammar and spelling mistakes, personally, I don't think registering is really important. But if you are going to add content, it's appropriate to register, so that people can identify X made this edit, and made this other edit 5 days ago. It builds a reputation.
2) You can click on your username at the top of the page (the link should be red), and create a userpage. Say who you are. You don't have to provide your real name, but can still tell people a little about yourself. Not everyone does this, but if you want people to know whether you are a 17 year old high school student, or a 50 year old professor, this is the place to do it. Once your userpage has been created, your username at the top of page will be blue. Any red link on Wikipedia means the page is empty.
3) When you add content, provide a source, or it might be deleted as unsourced content. You might be replacing unsourced content with your own unsourced content that you know is correct. However, other editors won't know this, and they might decide that sticking with the previous content is a better choice.
Two detailed instruction pages on:
1) How to edit a page on Wikipedia
2) how to cite sources