My failed attempt at adding Demographics to Google Analytics

Along with writing a blog I'm also now using Google Analytics to see the traffic on the blog. It gives you quite a bit of information - you can see the real time visits on your blog or the history of visits along with the information about the visitors language, country and also what platform the were accessing the blog from - a browser or a phone. I've also tried to add the 'Demographics and Interests Report', which according to Google tells you the age, gender and interests of your visitors. It actually turned out quite difficult to add it, so I started to look for help on Google Support and although they did have a guide as to how to enable the Demographics feature for a novice it wasn't very clear. Te next step for me then was the Internet. I looked for easy guides I could understand without complicated codes. Most of people were speaking very well about it, talking about its usefulness and showing how to use it to its fullest. However when it came to actually telling the readers how to enable it most were either just posting the link to Google Support page or simply paraphrasing exactly what Google said, like here. There was one blog that got me a little further, called 'Gravitate'. I managed to find the full code I'm supposed to replace in my blog code and found the old code on my blog code but there didn't seem to be a way to actually physically change the code. So, I have, in the end found the information I needed but wasn't able to do what I wanted, which is to enable the 'Demographics and Interests Report' in Google Analytics.