Let's try logging out of your Google account from your computer and also clearing your browser cache. Then, visit Google AdWords i.e. https://www.google.com/adwords/ and then logging in with your Google account.
If you are still redirected to AdWords Express, in the upper right corner of the screen, there is a drop-down menu link "Go to AdWords." Do this if the above solution do not work.
If both not work, you have to be contact AdWords Support, and have them look into the issue and help you remove AdWords Express and set up an account with AdWords.