A Golden Rule: Do not spend more than the value of the best house in your street towards your property renovation!
You need to make sure that you will recoup the planned investable amount in the renovation. The current property prices in your neighbouring area are a good indication of how much you should plan to invest or if you are uncertain of your neighbouring property prices, do the research at property websites, contact a local real estate agent or an architect who will be able to help you estimate how much to spend and what your returns may achieve.
An architect can work on the assets your house currently has, for example an architect may be able to help re-organise your floor space so you have more living area and less dividing walls. An architect will also help you utilise natural light and heat sources to achieve a more eco-efficient designed property.
Accessing the equity in your home will come down to the valuation of your property less the existing loan amount to arrive at the available equity. With accessing the equity you may split your loan, set up a line of credit or even refinance the whole facility to suit your requirements and lifestyle.