Yes, you can withdraw your agreement to the settlement agreement and ask to have your case set for a contested hearing. It is only non contested if you are both in agreement. A contested hearing means a trial to the court. If there are issues to decide that are important to you, you may want to have counsel represent you at hearing.
You can reach Harkess & Salter LLC at (303) 531-5380 or info@Harkess-Salter.com. Stephen Harkess is an attorney licensed in the state and federal courts of Colorado. This answer is for general information only and does not create an attorney client relationship between Stephen Harkess or Harkess & Salter LLC and any person. You should schedule a consultation with an attorney to discuss the specifics of your legal issues.
It is not really a matter of changing from an non-contested divorce to a contested divorce. All divorce cases are considered "contested divorces" unless and until both sides have signed a Separation Agreement which resolves each and every issue which must be addressed. Since your wife has refused to sign the Separation Agreement, you should put her on notice, preferably in writing, that you are withdrawing your agreement the the Separation Agreement. If you already have a non-contested hearing date, you need to ask the court to cancel that date and give you a date for a contested Permanent Orders hearing.
Beware of one possible pitfall -- if you case has been ont eh court's docket (list of active cases) for the last year and no one has submitted a separation agreement bringing things to an end, the case may have been dismissed. This is a rairy of counsel is involved, but for folks who don;t have attorneys, it happens with inactivity. You may want to check with the courthouse to see if your case is still alive. If not, you may need to re-file. There is also a chance you can re-kindle the old case, but to do that, you ought to consider sitting down with an experienced family law attorney in Colroado and discussing your options.
All my best.
In no way am I offering you legal advice, and in no way has my comment created an attorney-client relationship. You are not to rely upon my note above in any way, but insted need to sit down with counsel and share all relevant facts before receiving fully-informed legal advice. If you want to be completely sure of your rights, you must sit down with an experienced criminal defense attorney to be fully aware of your rights.