To do so add the following code to BeforeAdd/BeforeEdit events:
foreach ($values as $key=>$value)
$values[$key]=strtoupper($value);
return true;
If you also want all text to appear in upper case as it being entered add the following to 'Custom CSS' section in Style Editor.
.rnr-control input, .rnr-control select, .rnr-control textarea
{ text-transform: uppercase; }