In R, we can change the row names of a data frame using the rownames() function. The rownames() function takes two arguments: the data frame and a vector of new row names. Here is an example R program that demonstrates how to change row names of a data frame:

# create a sample data frame
df <- data.frame(x = 1:3, y = 4:6)

# display the current row names
rownames(df)

# create a vector of new row names
new_row_names <- c("A", "B", "C")

# set the new row names using the rownames() function
rownames(df) <- new_row_names

# display the updated row names
rownames(df)

In this example, we first create a data frame df with two columns x and y. We then display the current row names using the rownames() function. Next, we create a vector new_row_names of new row names. Finally, we set the new row names using the rownames() function and display the updated row names.

Note that the vector of new row names must have the same length as the number of rows in the data frame. If the vector of new row names has a different length, R will return an error.