You have to download the proper update (32 or 64bit) from the OP and copy the extracted files into your Lifeplay directory. You should be asked to overwrite many files. Confirming this should do the trick.
Got an issue too. When I try to add a relative, it's not working properly. A new person is spawned, has the right name and gets listed as relative. But when I encounter the person, I still have to exchange numbers. I wouldn't care, but when I actually do exchange numbers, a new person gets added to the contacts list. Wouldn't be tragic either. The problem is, whenever I get into a relationship with the relative, I end up having an relationship with that new person.