Depending on your specific needs—whether you want the official Sony developer tool or the community-favorite "Flashtool" by Androxyde—you can find downloads at the following locations:
For users on Windows 7 (32-bit), the official Sony flash tool is known as (or the Xperia Flash Tool). It is a desktop application designed for flashing standard Sony software onto unlocked Xperia devices. Official Download and Support sony flash tool 32 bit download windows 7