I have two dataframes. 
The First one is the original dataframe.
The second one is a changed dataframe (this data column could be changed by user).
I would like to update the df1 dataframe with df2 (changed data). 
Please refer to the expected result e.g1, e.g2
I really appreciate anyone's help.
# data frame 1 (orignal datas)
age <- c(24, 28, 31, 25, 27, 22, 29)
gender <- c("male", "female", "female", "male", "female", "male", "female")
score <- c(90, 80, 85, 75, 95, 80, 70)
df1 <- data.frame(age, gender, score, stringsAsFactors = FALSE)
df1
> df1
  age    gender score
1  24   male    90
2  28 female    80
3  31 female    85
4  25   male    75
5  27 female    95
6  22   male    80
7  29 female    70
# data frame2 (other data frame) - column could be changed by user
id <- c("1", "2")
ch_age <- c(50, 40)
ch_score <- c(80, 80)
df2 <- data.frame(id, ch_age, ch_score, stringsAsFactors = FALSE)
df2
> df2
  ch_id ch_age ch_score
1     1     50       80
exepcted result
e.g1 
  age    gender score
1  50   male    80 --> applied df2 dataframe this row
2  28 female    80
3  31 female    85
4  25   male    75
5  27 female    95
6  22   male    80
7  29 female    70
e.g2
  age    gender score
1  24   male    90
2  28 female    80
3  50 female    80 --> applied df2 dataframe this row
4  25   male    75
5  27 female    95
6  22   male    80
7  29 female    70
 
    