// to clear all picklist options
erm....

// to delete specific picklist options:
crmForm.all.field.DeleteOption(1);
crmForm.all.field.DeleteOption(2);
crmForm.all.field.DeleteOption(3);

// to add new picklist options:
crmForm.all.field.AddOption('Dem (in-house)',1);
crmForm.all.field.AddOption('Presentation (on-site)',2);

NOTE: adding new picklist options that do not otherwise exist will not be saved