Renault Laguna 94 solenoid is sticking?

Hi

I have had a comp check on my Renault Laguna 94 the solenoid is sticking and I am told needs replaced. I understand it is accessible. How do I replace it? Is this something I can do myself?
If it is a solenoid failure could this be caused by the oil loosing viscosity or having dirt in it?
Is it possible to check this.
Regards
Malcolm