This is how to change the KDE desktop icon size in SuSE. Red Hat may not work this way.
Run the Control Center (kcontrol). Click on Appearance and Themes, click on Icons, click on advanced, click on Desktop/File Manager, set Size, click on Apply. I don't think that Gnome has the facility to change desktop icon size through configuration settings. If so I have not found it yet.
You can change the size of the desktop icons on Gnome, KDE, and the login screen by changing the icon file that is being used. In SuSE almost every icon is supplied in several sizes, like 32x 32, 48x48, and 64x64. In both KDE and Gnome you can change the desktop icons by changing the properties of that icon. Instead of changing, say, the kwrite icon to a penguin, you can change the kwrite icon to a different size kwrite icon.
However, I think Tinkster is right that your problem is more likely that you
have the screen resolution set too small. Use xf86configure ( I think that is
what Red Hat uses) to change to a larger screen resolution.