You need to create a web set of fonts to replace the ones it currently uses. Go to this website Font Squirrel and build the set of fonts you would like to use. Once you have completed that, go to the fonts directory “catalog/view/theme/shoppica/fonts/” and paste the generated fonts in that folder.

Once that is done, go to the CSS file located “catalog/view/theme/shoppica/stylesheet/screen.css” and replace all of the default fonts listed.

I have changed mine to Helvetica…

@font-face {
  font-family: 'Helvetica Rounded Bold';
  src: url('../fonts/helvetica_rounded_bold-webfont.eot');
  src: local('Helvetica Rounded'), url('../fonts/helvetica_rounded_bold-webfont.eot?iefix') format('eot'), url('../fonts/helvetica_rounded_bold-webfont.woff') format('woff'), url('../fonts/helvetica_rounded_bold-webfont.ttf') format('truetype'), url('../fonts/helvetica_rounded_bold-webfont.svg#HelveRound') format('svg');
  font-weight: normal;
  font-style: normal;
}
@font-face {
  font-family: 'Helvetica Neue';
  src: url('../fonts/helveticaneue-extended-webfont.eot');
  src: local('Helvetica Neue'), url('../fonts/helveticaneue-extended-webfont.eot?iefix') format('eot'), url('../fonts/helveticaneue-extended-webfont.woff') format('woff'), url('../fonts/helveticaneue-extended-webfont.ttf') format('truetype'), url('../fonts/helveticaneue-extended-webfont.svg#Helvetica Neue') format('svg');
  font-weight: normal;
  font-style: normal;
}

You will also want to find and replace the rest of the CSS font-family entries too to match.