ggbilpot, How do I increase the factor label text size?

Question

I am struggling to change the attributes in my biplot created in ggbiplot. I would like to increase size of the text at the end of my factor arrows (the red text).

Can anyone help please?

The code I have used is as follows.

ma<- read.csv(file.choose(), header=TRUE)    
ma   
suba <- subset(ma, select=-c(X,Boat,Trailer, Boat.clean))
xa <-cbind(Frequency, Distance, Catchment,Items,Clean,Boat,Trailer, Boat.clean)
pa <- princomp(suba)
spa <-ggbiplot(pa) + geom_text(aes(label=ma$X), size=5, hjust=-.1, vjust=0, colour="1", groups = pa, ellipse=TRUE) + xlim(c(-2.4, 2))

ggbiplot example for stack: