If I have a house worth 1 million and decide to downsize to a house worth about 600,000, do I have to pay capital gains taxes on the remaining 400,000 or can I spend it as I please? thanks
So long as it is your principal private residence, then there is no CGT payable on the sale. Unless there is some element of development potential involved.
You do not have to spend any of the money from the sale of your home on a new home to avail of PPR CGT relief.
One you occupied the house as your main residence for the entire period of ownership (and there is no development element to the property) you will not have a CGT liability and can spend the proceeds as you like.