We always advise students to take the course they place into, regardless of which courses have been converted from transfer or AP/IB credits.
If you took the placement exam and you were placed in a lower level course than you have transfer/IB/AP credit for, you have two options.
1) You can dispute your score. Contact the advisor that corresponds to the course you were placed into for help determining what level course you need to enroll in. You can find a list of advisors here. It is always advised that you contact the appropriate advisor(s) if there are discrepancies between your placement and your transfer credit.
2) Contact the registrar’s office at email@example.com. You will need an override to register for a course you already have credit for. Often in this case, credit from your AP/IB exam will be assigned as elective credit at the 1XXX or 2XXX level as appropriate, thereby keeping courses from being duplicated. Alternatively, the registrar may adjust your transfer credits to instead convert as lower-level courses, avoiding duplication of credit for a given course. For example, say you have credit for SPAN 2001-2002-2003 due to an AP score of 5. However, you placed into SPAN 2002. You may ask the registrar to adjust your awarded AP credits to instead cover SPAN 1002-1003-2001, allowing you to enroll in SPAN 2002 without duplication.
Keep in mind that if you are approved to have overlapping credits (for example, having credit for both SPAN 2001 from AP and SPAN 2001 from a DU course), only one instance will be eligible to count towards a major or minor.