It also requires at least 2GB of memory and 8.8GB of storage space. MacOS Sierra requires one of the following Mac models and versions of OS X. Take a look at the information below to ensure that you meet all of the other necessary system requirements to upgrade to macOS Sierra, from our article: How to get macOS Sierra
Your current version of macOS can be updated to macOS Sierra.
If I'm understanding correctly, several apps are not working because you need to update your macOS.