I would have a little splash, nice holiday this summer for example.
Not tell anyone.
Think , gather info, plan
Probably:
Move to a house that suits in a nice area with access to everything I need, local shops, public transport, good schools, easy for work. Go mortgage free but not buy a house in excess of my needs.
Pay attention to my pension. Put in a sum, or plan to redirect mortgage payments into pension. Look into the tax benefits of paying into a pension .
Look for a good junior ISA for Dd and put a wodge in there for her in the future. Maybe put a full whack of Premium Bonds in her name. Or yours - for now, you can liberate them later.
Look at ways to best save for and fund for school fees if this is what you really want to do…or to have the money as a backstop if you get in a mess with state options.
Look at best way to manage the rest. Savings accounts: rates are high atm but you will be taxed on interest over £1000 (£500 if you are a high rate tax payer), ISAs are tax free. Premium Bond winnings are tax free.
In cash savings minus tax you could be making £20k Pa at current interest rates on £500k.
How much is your mortgage? What balance?
Concentrate on long term security, contentment and ability to fulfill ambitions.