Obtaining Lazarus

You can download Lazarus for Windows from Lazarus-IDE.org

There are two versions for Windows, 64 bits and 32 bits.
If you have Windows 64 bit and you only develop programs for your personal use, the choice is obvious.

But if you also intend to distribute your applications to other people, you don't know what version of Windows they are using, so you'd better stay on the safe side and install the 32 bits version of Lazarus.