Increase the Maximum File Upload size in SharePoint 2013

The default max single file upload size is 50 MB by default for a web application (in IIS 6.0)and the  default max single file upload size is 28 MB by default for a web application (in IIS 7.0). 

In order to increase the maximum file upload size , please make the following change in central Administration

1. Go to SharePoint Central Administration > Application Management'.
2. Under SharePoint Web Application Management, click 'Web application general settings’.
3. On the Web Application General Settings page, choose the appropriate web application.
4. Under Maximum upload size, type the file size which you want to upload and click on OK. You can specify a maximum file size up to 2,047 megabytes.

Another important changes is to modify web.config file.This change will add timeout to the runtime tag.

1. Open the web.config 
2. Replace the below tag   <httpRuntime maxRequestLength="51200" />
3. <httpRuntime executionTimeout="999999" maxRequestLength="51200" />