i have two assembly version
old version is
new version
if i want to use old version what should i do?
if i want to use new version what should i do?
in which field i have to mention in assembly info file ?

The assembly is referenced in your project references which can be managed using the IDE.

As far as deciding to use which version, you need to compare them:

private static VersionCompareResult CompareAppVerToDbVer()
      using (DataTable dt = DatabaseSetup.GetSystemReg())
        if ((dt == null) || (dt.Rows.Count == 0))
          return VersionCompareResult.NotSetupYet;

        int i1 = (int)dt.Rows[0]["Value1Num"];
        int i2 = (int)dt.Rows[0]["Value2Num"];
        int i3 = (int)dt.Rows[0]["Value3Num"];
        int i4 = (int)dt.Rows[0]["Value4Num"];
        Version dbVer = new Version(i1, i2, i3, i4);
        Version softVer = new Version(Application.ProductVersion);

        int compResult = softVer.CompareTo(dbVer);

        if (compResult > 0)
          return VersionCompareResult.Newer;
        else if (compResult < 0)
          return VersionCompareResult.Older;
          return VersionCompareResult.Same;

i dint get u ..if i want use old and new version of assemblies what are the properties and what are the fields i have to change in assemblyinfo file?
what is the use of binding redirect?