Increase size of axis labels in ternary diagrams using ggtern

I would like to increase the size of the ternary diagram, when using the following code:

# Dataset
NP_Mobj
    EE   ES   SE id
1 0.15 0.25 0.60  1
2 0.30 0.20 0.50  1
3 0.15 0.15 0.70  1
4 0.40 0.20 0.40  1
5 0.70 0.10 0.20  1
6 0.50 0.30 0.20  1
7 0.32 0.20 0.48  2

idNP  <- "1";   idMObj <- "2";
Group <- as.factor(NP_Mobj$id)
 IWRM_Trinagle_NPCriteria_MObj <-  ggtern(NP_Mobj, aes(
    x = SE,
    y = EE,
    z = ES
  ))                                                    + 
    geom_point(aes(color = Group ), size = 8)           + 
    theme_showarrows()                                  +
    labs(xarrow = "Social equity (SE)",
         yarrow = "Economic efficiency (EE)",
         zarrow = "Environmental sustainability (ES)")  +
    scale_colour_manual(breaks = c(idNP, idMObj),
                        values = c("black", "red"))     +
    theme_clockwise() + theme_bw()
IWRM_Trinagle_NPCriteria_MObj <- IWRM_Trinagle_NPCriteria_MObj +  theme(legend.position="none")

I would like to increase the size of the three axis labels and the axis values.

You can use the axis.title and axis.text arguments of theme() to change the appearance of axis titles and texts.

library(ggtern)
ggtern(NP_Mobj, aes(
  x = SE,
  y = EE,
  z = ES
))                                                    + 
  geom_point(aes(color = Group ), size = 8)           + 
  theme_showarrows()                                  +
  labs(xarrow = "Social equity (SE)",
       yarrow = "Economic efficiency (EE)",
       zarrow = "Environmental sustainability (ES)")  +
  scale_colour_manual(breaks = c(idNP, idMObj),
                      values = c("black", "red"))     +
  theme_clockwise() + 
  theme_bw() +  
  theme(legend.position="none", 
        axis.text = element_text(size = 18),
        axis.title = element_text(size = 20))