There are two different ways to zoom in Gantter.

The first way is Gantter's zoom functionality which is using the "Zoom In" or "Zoom Out" buttons on the toolbar or in the View menu of the Gantter editor. This changes the time periods of your Gantt chart and allows it to go from a monthly view to a weekly view. 

However, if you want to zoom in on the entire project as a whole, you can use your browser's zoom functionality.

[If you use Chrome, please see the following link for how to zoom in Google Chrome: https://support.google.com/chrome/answer/96810?hl=en ]