Pruning croton

Hi, we got a croton it's been in a south facing bathroom for 4 years now. Its generally healthy but it's growing quote tall now and seems to have one main stem. I want to prune it to reduce the height. How do I go about it? I asked at my local garden centre and one person said you can't prune it and other said no problem with cutting of main stem to reduce height so not sure..

I aam not sure exactly what variety of croton I have but it's one which has shaped leaves the other pointy end of that makes sense.. 

Thanks