How do I change a single value in a data.frame?

Could anyone explain how to change a single cell in a data.frame to something else. Basically I just want to rename that one cell, not all cells which matches it. I can´t use the edit() command because it will screw up my script since im using the data.frame on several occasions.

Thanks in advance

data.frame[row_number, column_number] = new_value

For example, if x is your data.frame:

x[1, 4] = 5

Suppose your dataframe is df and you want to change gender from 2 to 1 in participant id 5 then you should determine the row by writing "==" as you can see

 df["rowName", "columnName"] <- value
 df[df$serial.id==5, "gender"] <- 1