There's 3 variables you can change to do that. Look in either the globalVariables.inc file in the inc folder or look in the [Variables] section in the skins .ini file if it doesn't have the globalVariables.inc file. Look for the following 3 variables:
FontSizeTitle=8 (Size of the title, i.e. "Deepbit" or "BTC Guild")
FontSizeGeneral=7 (Size of all the stats and stuff)
FontSizeBars=6 (Size of the text on the worker bars)
Change those to your liking
Depending on how large you go it may cut off some text in places or hang outside the background image. So you may also want/need to change it's size also, which can be found under [Background] in the main skin .ini file. Just increase the H (height) and/or W (width) values to whatever suits your needs. You may have to also change all the Y values for things as well to space out the individual stats (so they aren't all overlapping when the text gets larger).
Also, I'm not sure if you're running Rainmeter on your miner's machine or some other machine that you're remoting to for a specific reason, but if you didn't know you can run this on your main computer. It doesn't actually have to run on your mining machine. I run this skin on my main computer, but mine on a 2nd computer. You may already be aware of that, but this is just a friendly heads up if you didn't know
You could actually run this skin on your main PC, your miner, a laptop and your computer at work all at the same time if you felt like it and they all would display the same information