You have a couple of options here. To be clear though, legally you are both owners, just because you are a majority owner you don't necessarily have more rights.
With a property that is jointly owned, you can either:
a. agree to buy out the other party at market value of their share; or
b. sell the property and divide the proceeds according to the trust declarations, i.e. 80/20.
It's not an option simply to do nothing, unless the other party is happy for this to be the case. But, even if they agree to do nothing now, if they decide in the future that they want their money and you can't buy them out, then they would succeed in going to court for an order for sale, I'm afraid.
I hope that this answers your question?
Thank you for your enquiry today. I am happy to answer follow-up questions - please do get in touch with requests for extra information or further queries and I will do my best to help you.