Your succulent (Euphorbia tirucalli) does not like trimming at all - but must is must.
You can find some useful information there :

www.euphorbia.de

Milin

PS. I like your plant very much - it looks healthy and well cultivated.

Attention for the sap as it is very poisonous. Avoid contact with skin, mounth and eyes!!! Wear gloves.

Thanks to everybody for their input.