I am a PhD student with a six months initial contract. What do I need to do to get my contract extended?

The initial duration of the association contract is 6 months. The contract may be extended by two periods of 12 months, followed by a last extension of 6 months. The maximum duration of a doctoral student contract may not exceed three years. 
A progress report on the student's work is required for extensions after 18 months and after 30 months.