A macro is not correct tool. But VBA along with query should be. Still won't be simple. Following is example query to determine which names are duplicated:
SELECT IIf(InStr([title],"."),Left([title],InStr([test],".")-1),[title]) AS T, Count(ID) AS C
FROM tablename
GROUP BY IIf(InStr([title],"."),Left([title],InStr([test],".")-1),[title]);
Automating deletion would be tricky part - review http://www.accessrepairnrecovery.com...crosoft-access. However, that method will not account for different categories (if that has happened for same file) because aside from variation in filename, different categories actually make records unique. You will have to make case-by-case decision on which category should be retained.
Should a lecture be allowed multiple categories? If yes, then need a related dependent table (or {yuck} use a multi-value field). Are there already related tables dependent on this one?
Standardize data - either all should have extension or none.