I respectfully disagree with the two previous posters. You should investigate and correct errors regardless of your credit score.
https://www.annualcreditreport.com
There are many companies that will sell you your own credit report. Some may offer credit monitoring services as well. I cannot comment on those.
Regardless of where you get your credit report from, there are 3 bureaus that maintain your report. See link above.
You may want to print out your report and read it very carefully. Circle/highlight anything you find inaccurate. Anything at all.
Identify which of the three bureaus provided the inaccurate information. If more than one reported the error make a note of that as well.
What you want to do is contact the original creditor that reported the error, as well as the bureau(s) that maintain the error. Most of the time the creditor will correct it for you and mail you a letter. I would follow up and make sure that the bureaus gets the correction.
You can usually find the creditor's contact information on the report itself. If not try Google and see if you can find a customer service number.
The 3 credit bureaus' contact information is usually listed on the credit report itself, or you can find them on Google as well.
Typically it takes a really long time to correct errors so be aware.
Other than correcting errors on your credit report, I do not suggest trying to tweak your credit score.