You can use the package lubridate to convert to a date with ymd then format it for the way you want it displayed
Dates_df <- mutate(Dates, dli = format(ymd(dli), "%Y/%b/%d")
(I use dplyr here, I assume you have other variables in Dates)
without dplyr if you just want to keep the dates in a vector:
Dates_vec <- format(ymd(Dates$dli), "%Y/%b/%d")