Uuumm..I don't know how to do that.† *blushes*
Just pull up the character portrait you were using on RPOL. Then right-click your mouse and select Save As. Try this on my portrait right now to see how it works. Iím not sure about Macs or other platforms, but if youíre on PC then by default it should save the picture in your Documents folder or My Pictures (a subfolder of My Documents). Remember which folder you saved it to!
Then go to edit your profile here. When you get to your profile section, click Forum Profile Information. Click the option- I will upload my own picture. Then hit browse to pull up your picture. Then hit Change Profile at the bottom to upload your image.
If youíre having a struggle getting this, then Iíll assume you donít have portraits stored on the web anywhere. If you did, then you should click I have my own pic to link to them.