A possible solution for low computer performance would be storage. It is very easy to overlook how much memory that you have used up. Here is a fast and easy way of checking how much storage that your apps and files are taking up.
Settings > Storage > My PC (Or your selected Drive)
Apple Menu > About This Mac > Storage > Manage
From here, a list of categories will show up. Each category has a bar next to it representing how much storage it is taking up. Click one and it will give you a more detailed list of items in that category that you can select to delete or uninstall.