how to change columns name from a other dataframe

Question

hi i have a data that looks like that:

    x            y_1    y_2     y_0
0   2001-04-19  100.0   100.00  NaN
1   2001-04-20  98.6    99.98   100.0
2   2001-04-21  98.6    99.98   100.0
3   2001-04-22  98.6    99.97   100.0
4   2001-04-23  97.3    99.30   100.0

and an other dataframe that looks like:

    balloonText                 valueField
0   Haussmann Actions Europe    y_0
1   MSCI Europe NR              y_1
2   Act. Europe                 y_2

I would like to replace in the first dataframe the column name (except x column which will be date) with the balloonText columns of the second one How can I do this ?

I have to add that the number of columns of the the first df (and also the number of rows of the second) can change.