[OSM-newbies] changing one node into a roundabout

[mariner]

Hi  there,

Today I found a crossroad on the map where a roundabout should be.

All the ways are ending up in one node. But I'd like to have a circle of
at least 4 nodes. How can i change that with a small amount of mouse
clicks? (in JOSM)

thanks for your reply..
mariner