Your Legal Right to Switch
Colorado Rules of Professional Conduct are clear: a client has the right to discharge their attorney at any time, with or without cause. The retainer agreement does not override this right. While the retainer may include language about fee obligations for work already performed, it cannot prevent you from leaving. Any attorney who tells you that you are "locked in" or "cannot leave" is either misinformed about their ethical obligations or being deliberately misleading.
The terminated attorney may assert a lien on the case file for fees and costs already incurred. In practice, this is almost always resolved at the time of settlement: the new attorney and the old attorney negotiate how the contingency fee is split based on work performed. You do not typically pay out of pocket for this. The total fee you pay usually remains the same (33% or 40%), with the two firms dividing that fee between them based on their respective contributions.