Get the handle to the line using:

hline = findobj(gcf, 'type', 'line');

Then you can change some property for all the line objects:

set(hline,'LineWidth',3)

or just for some of them :

set(hline(1),'LineWidth',3)

set(hline(2:3),'LineStyle',':')

idx = [4 5];

set(hline(idx),'Marker','*')

This is not an original post. Here is the original post

hline = findobj(gcf, 'type', 'line');

Then you can change some property for all the line objects:

set(hline,'LineWidth',3)

or just for some of them :

set(hline(1),'LineWidth',3)

set(hline(2:3),'LineStyle',':')

idx = [4 5];

set(hline(idx),'Marker','*')

This is not an original post. Here is the original post