A simple explantion of releasing equity through re-mortgaging is as follows
You have a house that was bought for €200,00.
You have a mortgage of €150,000 (equity of €50,000).
The house is now worth €250,000, but your mortgage is still €150,000, so you now have equity of €100,000.
You can increase your mortgage to €200,000 and realise the additonal €50,000 equity (if your lender would allow you, and if you can afford it, you could realise more) to use as a deposit for your own home.
You appear to have equity of €360,000 in your investment property. However, that assumes that the bank agree with the valuation of €500,000, and as PM1234 says, there are other factors that they will consider when looking at an application to remortgage/release equity.
Of course you will have a higher mortgage repayments after increasing the mortgage on your investment property, and a greater risk of negative equity.
You may wish to take professional advice on this course of action.