I can not find in application folder
conf.json to change client from full to lite.
Where is the configuration file can be found in Windows XP
When you say application folder, do you mean %LOCALAPPDATA%\byteball? That's where you should try looking. Having said that, you can not change a client from full to light and vice-versa. You have to reinstall and chose light.
When I tried to reinstall...
I've got error:

System: Windows XP 64 bit.
I can provide the necessary logs.
If you had a full node before, then if you reinstall directly, it will not work with the current content of your %LOCALAPPDATA%\byteball folder (full and light do not have the same databases). You should transfer your funds to another device, uninstall the app (potentially remove %LOCALAPPDATA%\byteball manually if the uninstallation leaves it) and then install and chose light and finally move back your funds. As far as I know, that's the only way. If you do that, keep a copy of %LOCALAPPDATA%\byteball and your seed just in case.