How to change the Logo size in header

I’m using a theme called “Cynic” for my wordpress website “gwmshealth.com”.
When i replaced teh demo logo with original one, it appears smaller on both desktop and mobile. I don’t know how to increase its size so that it looks appropriate.
Do i need custom CSS to do it? If so then what code should i use?
@Axilthemes

Hi,

Contact with your purchase item author hope they will help you out from your issue.

Thanks!