ok :) Thank you everyone for reading my question, but I solved the problem. The code that solves the problem it's following:
using Microsoft.Reporting.WinForms;
ReportParameter[] param = new ReportParameter[1];
param[0] = new ReportParameter("ParameterName", "ParameterValue", false);
reportViewer1.LocalReport.GetParameters();
reportViewer1.LocalReport.SetParameters(param);
That's all.
Have a great day,
Sandu