[R] How to decrease size of points?

[Medic]

№1 Medic:
The code works as I want, but the points (circles) on the plot are too
big. How to decrease them? Where to insert (for instance) size = 0.8
for points (circles) on plot?

p1 <- p + geom_point(aes(size = Stage), alpha = 1/3) + xlab ("X") +
ylab("Y") + geom_smooth()

Stage is factor, x and y - continuous
===
№2 Rui Barradas:
add the scale_size
p1 + scale_size_manual(values = 0.8)
===
№3 Medic:
Thanks Rui, but I got:
Error: Insufficient values in manual scale. 12 needed but only 1 provided.
(or Error: Continuous value supplied to discrete scale)
===
№4 Rui Barradas:
Try
nsize <- length(unique(df1$Stage))
before the plot and then
p1 + scale_size_manual(values = rep(0.8, nsize))
===
№5 Medic:
Rui, your example is very good!
Now your code works, but not as I want.

Why did I use:
geom_point(aes(size = Stage)...?
In order to receive points of DIFFERENT size!

And what does your code do?
It assigns the same fixed size to ALL points.

I don't need this.
I sincerely thank you and closing the topic!