Run the installer. If you get an error about "failed to download Roblox," your version is too new. Go older.
: Roblox dropped XP support after version 2.447.385 (around 2017–2018). Trying to install a modern Roblox client on XP will fail. windows xp roblox download
A recent processor (released after 2005) with at least 1.6 GHz. Graphics: DirectX 10 or higher feature level support. Memory: 2 GB of RAM minimum (4 GB recommended). 2. Can You Still Download Roblox for Windows XP? Removing Support for Windows XP Users (Studio Only) Run the installer