DeleteFiles

public static class DirectoryInfoExtensions
{
    /// <summary>
    /// Delete files in a folder that are like the searchPattern, don't include subfolders.
    /// </summary>
    /// <param name="di"></param>
    /// <param name="searchPattern">DOS like pattern (example: *.xml, ??a.txt)</param>
    /// <returns>Number of files that have been deleted.</returns>
    public static int DeleteFiles(this DirectoryInfo di, string searchPattern)
    {
        return DeleteFiles(di, searchPattern, false);
    }

    /// <summary>
    /// Delete files in a folder that are like the searchPattern
    /// </summary>
    /// <param name="di"></param>
    /// <param name="searchPattern">DOS like pattern (example: *.xml, ??a.txt)</param>
    /// <param name="includeSubdirs"></param>
    /// <returns>Number of files that have been deleted.</returns>
    /// <remarks>
    /// This function relies on DirectoryInfo.GetFiles() which will first get all the FileInfo objects in memory. This is good for folders with not too many files, otherwise
    /// an implementation using Windows APIs can be more appropriate. I didn't need this functionality here but if you need it just let me know.
    /// </remarks>
    public static int DeleteFiles(this DirectoryInfo di, string searchPattern, bool includeSubdirs)
    {
        int deleted = 0;
        foreach (FileInfo fi in di.GetFiles(searchPattern, includeSubdirs ? SearchOption.AllDirectories : SearchOption.TopDirectoryOnly))
        {
            fi.Delete();
            deleted++;
        }

        return deleted;
    }
}

DirectoryInfo di = new DirectoryInfo(@"c:\temp");
di.DeleteFiles("*.xml");  // Delete all *.xml files 
di.DeleteFiles("*.xml", true);  // Delete all, recursively