It looks as though the answer to my question is here;
http://stackoverflow.com/questions/727123/update-asp-net-membership-from-windows-service
However I cannot get any recognition for the namespace; System.Web.Security. I try to add a reference to System.Web and I get;
Could not resolve assembly "System.Web". The assembly is not in the currently targeted framework ".NETFramework,Version=v4.0,Profile=Client". Please remove references to assemblies not in the targeted framework or consider retargeting your project.