Replacing specific characters of a filename every month. Please Help!!

Hi

I have 10 & ”xls” files saved in 1 folder and 5 sub-folders, which
have filenames suffixed with common characters. I replace these characters
month-on-month.

Can anyone please help me by writing a macro for replacing these characters of a filename?

For, e.g,

Folder > sub folder > report name

1. 2011 > Revenue Reports > report name_1 Aug-11.xls
2. 2011 > Revenue Reports > report name_2 Aug-11.xls
3. 2011 > Marketing Reports > report name_3 Aug-11.xls
4. 2011 > Marketing Reports > report name_4 Aug-11.xls
5. 2011 > Expenses Reports > report name_5 Aug-11.xls
6. 2011 > Expenses Reports > report name_6 Aug-11.xls
7. 2011 > Sales Reports > report name_7 Aug-11.xls
8. 2011 > Sales Reports > report name_8 Aug-11.xls
9. 2011 > Billings Reports > report name_9 Aug-11.xls
10. 2011 > Billings Reports > report name_10 Aug-11.xls

As I have explained at the top, I’ll have to monthly change the month name manually (in above e.g., from "Aug" to "Sep"); which i wish could be automated using macros.

Can we have a command included in this macro that searches for "xls" files at the main folder level i.e., "2011" folder and this search will consider all the 10 files that are in different sub-folders inside the main folder "2011".