Structure

Hi folks,
how do I go about amending '.' to either '-' or '_' (I need the files to match an existing structure that I have). For Example:
Companyname_yy.mm.dd_Firstname.Surname_Title-of-Project.extension
how do I go about amending '.' to either '-' or '_' (I need the files to match an existing structure that I have). For Example:
Companyname_yy.mm.dd_Firstname.Surname_Title-of-Project.extension