Credit Given to Same Name, Wrong Person - how do I correct this?

Go to the movie and use the Edit page button at the bottom. In the Cast drop-down box at the top, select Correct/Delete and then click Continue. Now find the credit that is wrong, and choose "Correct" in the box next to it. If you already have a page on IMDb use the name from that page exactly, such as removing (I) at the end of the name and replacing it with (II), if that is your page. If you don't have a page, delete the number at the end of the name, and then click on the Re-check these updates button. You will then be presented with a list of actors with that name, and  below those an option to add a new one with the same name. It might be wise to check the checkbox for providing an explanation for your change, and explaining the situation as you have here.

In your case, since there is only a single Louis Tucci in the database at the moment (and assuming you are not Lou Tucci), you should follow cartman_1337's instructions, with these specific changes:

When you are able to actually make the change to the name, you need to change it to Tucci, Louis (II) - i.e. add (II) at the end.

After the Re-check you should check the radio button beside This is a different person not currently listed - create 'Tucci, Louis (II)'.

An explanation is very important in these case. You should indicate that you are the person who played this part, but are not the person currently listed, so you are creating a new name.

P.S. The Roman numeral is used to distinguish between various people with the same name. It is generally assigned in the order in which the people are added to the database, and says nothing about relative importance. Once your name is created, the current name will be changed to Louis Tucci (I)