We have a lot of clients, particularly those who run some sort of cloud drive like Dropbox, complain about their hard drives running out of space. Over the past few years, Apple has made it very difficult to upgrade your computer yourself. Even if you knew how to do it, you may not want to run the risk of opening up your computer for a hard drive replacement. Well you're in luck.
There are various manufacturers that have made elegant solutions to give you up to 512gb more internal memory through an SD card. There is no installation. You simply slide the sd card into your computer and you now have a second internal hard drive! You can use this to store your iTunes library, Photos library, Dropbox or Google Drive folders. This will free up your internal space to ensure that your mac doesn't come to a grinding halt every few days forcing you to delete otherwise necessary files.
Transcend is the leader in this field and our customers have been very happy with the results. You can find the various options here.