ggplots2 ggsave text size not changing

Question

I'm having issues with changing the size of the title, X-Y labels, X-Y axis text for my ggplot2. I'm using ggsave to save the plot as a jpg.

p <- ggplot()
p + theme(axis.title = element_text(size=30), axis.text.y = element_text(size=30),
          axis.text.x = element_text(size=30))

but changing the sizes of these texts doesn't change anything on the plot. Would anyone know how to properly change the text sizes?

---

So I fixed the issue I was having so the changes I make to theme are not affecting the plot (I've tested with changing text color), however the size of the axis text still does not change.

p <- ggplot(d[d$user==i,], aes(x=date, y=url, group=user, label=user)) + geom_line() + geom_point() +
  labs(list(title=i, x="Date and Time", y = "URL")) +   # Plot labels
  axis.POSIXct(1, at=seq(daterange[1], daterange[2], by="hour")) # Set x axis range to first and last date-time in data
p <- p + modifiedtheme
ggsave(plot = p, filename = "sample.jpg", height=2, width=6)

Answer 1

Here is a minimal, fully reproducible version of the problem (or lack of any problem, as comments have pointed out). Your own posted code appears to be correct, but maybe this example will help you solve whatever the real problem is:

library(ggplot2)

p1 = ggplot(iris, aes(x=Sepal.Length, y=Sepal.Width, colour=Species)) + 
     geom_point()

p2 = ggplot(iris, aes(x=Sepal.Length, y=Sepal.Width, colour=Species)) + 
     geom_point() + 
     theme(axis.title=element_text(size=30))

ggsave("figure1.jpg", plot=p1, height=3, width=4, units="in", dpi=150)
ggsave("figure2.jpg", plot=p2, height=3, width=4, units="in", dpi=150)