The thickness of the line cannot be increase more as it's a combo chart. The expression settings for High Stock, Low Stock, Stock close etc are grayed out and hence you cannot increase the size of line. Even going in expressions of line will not work here <W5>
As far as squares and circles concern on your chart you may increase the size by going Properties > Presentation Tab (Line Width, Symbol Width, Trendline Width)
Please find the attached qlikview app.
I hope this is informative.
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