Hi Kamen,
To set the line width you can use the following code
this.chartControl1.Series[0].Style.Border.Width = 5;
and to set the linetype use the following code,
this.chartControl1.Series[0].Style.Border.DashStyle = DashStyle.DashDot;
Refer the following sample that comes with the install that demonstrates various setting that can be done with a line chart,
\My Documents\Syncfusion\EssentialStudio\5.1.0.51\Windows\Chart.Windows\Samples\2.0\Chart Gallery\Line Charts\LineChartSample\cs
you can also go through the documentation available at the following link.
http://www2.syncfusion.com/ug/Default.aspx##Essential%20Studio.chm/ChartWindows/LineCharts.htmlKindly take a look and let me know if you need any further assistance.
Regards,
Ajish.