[Solved]-High Charts: Change each individual plot/marker size, is it possible?-Highcharts

Add lineWidth parameter in series list. See this jsFiddle code. Crucial code:

var chart = new Highcharts.Chart({
    // some other code
    series: [
        {
            name: 'Tokyo',
            data: [7.0, 6.9, 9.5, 14.5, 18.2, 21.5, 23.3, 18.3, 13.9, 9.6],
            lineWidth: 5
        }, {
            name: 'New York',
            data: [-0.2, 0.8, 5.7, 11.3, 17.0, 22.0, 20.1, 14.1, 8.6, 2.5],
            lineWidth: 15
        }
    ]
}

Also see the documentation for possible parameters.

//EDIT

You can also change markers size on whole chart or single points. See this jsFiddle. And the code:

var chart = new Highcharts.Chart({
    // some other code
    series: [
        {
            name: 'Tokyo',
            data: [7.0, 6.9, 9.5, 14.5, 18.2, 21.5, 23.3, 18.3, 13.9, 9.6],
            // marker setting for all points in this series
            marker: {
                radius: 5
            },
            lineWidth: 5
        }, {
            name: 'New York',
            // marker setting for second point only
            data: [-0.2, { y: 0.8, marker: { radius: 15 }}, 5.7, 11.3, 17.0, 22.0, 20.1, 14.1, 8.6, 2.5],
            lineWidth: 15
        }
    ]
}