From the menu structure, click on Microsoft Dynamics GP > Tools > Setup > Financial > Multicurrency
In the Multicurrency Setup window, lookup a currency in the Functional Currency field. That form will look something like this:
When you press OK, you'll get this warning:
So, we'll need to run checklinks as follows:
Click OK, and you'll get the progress form below while processing. When finished, you'll get a report; in my experience the report is always empty.
All set!