I think I messed up with uni choices

I put a uni as my firm because it had higher entry requirements than the one I felt more welcome, warm and wanted to go to, I just found out that I cant decline a firm if I meet the requirements. Would it be a good idea to transfer when the year starts if I meet the grade requirements as I don't know what I was thinking when I chose them I just did it on a whim and I regret it.

Is it too late to change - I think you can ask your "firm" to release you - but first check that your insurance would be happy to become your firm. A couple of phone calls could sort this out?

You should sort this out now rather than waiting. Firstly, phone UCAS and tell them that you are going to be trying to swap your Firm and Insurance around. Next, phone your Insurance and ask if they will mind becoming your Firm (they'll probably be only too happy) and then phone your current Firm. Once both Unis have given permission, you will be able to make the swap and UCAS will help you.