I'm not sure exactly what you mean by "according to required desire" (which sounds weird in English), so I'm going to assume that you mean "aesthetically".
I'd do the following, which I've listed in decreasing order of aesthetic importance (which is of course a matter of personal judgement):
- Change the gridlines color from black to gray.
- Change the gridlines thickness from 1 to 0 (which isn't as small as it sounds).
- Add thickness= 2 to the main part of the plot.
- Change the labelfont to ["TIMES", "BOLDITALIC", 13]. The u in Helvetica looks weird to me because its descender (bottom right corner) is barely visible.
With just those very easy changes, I get this:
With a bit more effort, a legend can be added:
kQs:= k=~ .1*[$4], Q=~ [.5615, .4989, .4365, .3742]:
subs~(kQs, M= .2, N= 2, x= 0, u), eta= -1..1,
color= [black, red, blue, green],
legend= ``~(kQs), legendstyle= [location= right, font= ["TIMES", 8]],
labels= ['eta', 'u'], labelfont= ["TIMES", "BOLD", 13], size= 200*[3,2],
axis= [gridlines= [8, thickness= 0, color= gray]]