Open the Start menu and click on the "Printers and Faxes" icon. This will open a window with a list of the printers currently set up on your computer.

Double-click on the icon of the printer you want to change to online. A pop-up window detailing all current print jobs will open.

Go to Printer in the menu bar of the pop-up window and uncheck "Use Printer Offline." This action will change the printer from offline to online.

Open System Preferences by clicking on the icon in the Dock.

Go to the Print & Fax control panel under the Hardware category.

Select the printer you want to take online from the list on the left side of the screen. Then click on the "Open Print Queue" button.

Click on the "Resume Printer" button at the top of the queue window to change the printer from offline to online.