This has been one of the repetitive questions we have received in our support ticket.
This is most likely an issue with your hosting’s default upload size. There are many articles out there to fix this issue.
We have added one of the article which we feel is better and easy to understand: http://www.wpbeginner.com/wp-tutorials/how-to-increase-the-maximum-file-upload-size-in-wordpress/
Kindly follow the steps given in the article above. It should fix your issue.