The reason you're being asked for a reprex, or for some non-image source for your data is that it's much easier to help you if we have the code. Here's one solution using the aforementioned hex2dec() function, and mutate_all() from dplyr.
Note that column names that start with numbers are not syntactically valid in R, so they have to be surrounded by backticks.
library(broman)
hexdf <- tibble::tribble(
~`1`, ~`2`, ~`3`,
"1A", "15", "18",
"16", "1F", "13",
"1D", "19", "1B"
)
dplyr::mutate_all(hexdf, hex2dec)
#> # A tibble: 3 x 3
#> `1` `2` `3`
#> <int> <int> <int>
#> 1 26 21 24
#> 2 22 31 19
#> 3 29 25 27
Created on 2019-12-02 by the reprex package (v0.3.0.9001)
To "save" the output, you can create a new data frame/object by assigning it a new name, or you can overwrite the hexdf object you created at the beginning.