Correct Fonts on HTML file

Hello I had work done by a developer on here who did not complete the work that I needed done. So there is one change that I need made but I myself cannot get it to work so I need the help of a developer who can correct a simple mistake. What is needed to be done is simple - I need a certain font on my html file replaced with another one. The problem was that the font was not a web font and the developer did nothing about this. I have converted and downloaded my font from here - [login to view URL] and it is gotham-light. The developer did not implement it and i need the corrected as the design is not showing correctly on the internet due to the font not being in the files. This should only take 20 mins to edit the CSS and HTML code and add the files into the correct place. Many Thanks