Welcome to the forums. There is a way I've been told, but it will not be easy. What I do know is you will loose a lot of the map as there is no RedPower 2 for 1.5.2 and that had world generation. You will probably have huge holes in the ground where marble had once generated and any of the basalt volcanoes will now be nothing, but a lava spout with nothing surrounding it. You will loose all your RP2 and XyCraft machines, tanks and anything else related to those mods that does not have another mod adding it in 1.5.2 Suffice it to say anything that was added by mods that were in Ultimate that are no longer in Unleashed will disappear. The easiest and probably most practical thing to do is to start over or keep playing Ultimate.
