By being released into Clearing you will lose your firm and insurance university places. To go to your insurance university, you will need to be released into Clearing and then taken up in Clearing by your insurance choice, as a Clearing applicant.
You should call your insurance university, explain your situation - that you would to take up your place at their university and not your firm choice university - and they will be able to provide confirmation of whether there is space available for you on your chosen course. Your insurance choice provides confirmation that they will take you through Clearing (they may provide a Clearing offer or reference), then you should then visit UCAS Track to explore your options under "Decline my place". Please be aware that declining a UF offer may be irreversible, so please do check the guidance carefully before you make your final decision.