[SunHELP] Just rename file

If I want to rename the files at the same time, same pattern
Ex.
I have these file.
file.xxx-day.png
file2.xxx-week.png
file3.xxx-month.png
file4.xxx-year.png

want to change it to be

file.yyy-day.png
file2.yyy-week.png
file3.yyy-month.png
file4.yyy-year.png

Is that anyway to rename these files at the same time,
to save typing from 'mv' for each file. 
Because now I have a hundreds of this kind of  files.

Thanks,
pat.