You just need to change set "font-size" for the labels in question. This one seems more straight forward than your other recent request so if you could provide details on which labels you want changed and which size you want, I can probably provide the CSS for you.
I would like the the labels saying venue, location and etc. and the parts in that gray header saying Final positions and Tournament statistics and etc. to kinda a size of this infobox but if you want more specifc mesures, I think this template might help.