
TL:DR, there are two ways to quickly fix this problem for users running OS 2.4.2 and below:
1) You can DOWNLOAD the new OS from Raspberry Pi
OR
2) Manually updating the repository link by performing the following command
Change the word "jessie" you see in the following text documents to "stretch"
sudo nano /etc/apt/sources.list
sudo nano /etc/apt/sources.list.d/raspi.list
After saving the text documents, perform the following commands
sudo apt-get update
sudo apt-get dist-upgrade