assuming your model has some name like gbmFit1 find out what parts of the object take up space
library(tidyverse)
library(lobstr)
imap_dfr(gbmFit1,~tibble(size=obj_size(.x),name=.y)) %>% arrange(desc(size)) %>% print(n=Inf)
if its for example trainingData, and you want to throw it out ..
gbmFit2 <- gbmFit1
gbmFit2$trainingData <- NULL
# test if still work as a model post our excision
predict(gbmFit2,newdata = testing)