Lubuntu uses the LXDE Desktop Environment which in turns makes use of PCManFM to manage the desktop. Therefore in order to change the size of the desktop icons you need to access PCManFM Preferences and set the desired icon size.
Open PCManFM and Go to Menu → Edit → Preferences → Display tab
Lubuntu uses the LXDE Desktop Environment which in turns makes use of PCManFM to manage the desktop. Therefore in order to change the size of the desktop icons you need to access PCManFM Preferences and set the desired icon size.
Open PCManFM and Go to Menu → Edit → Preferences → Display tab
Enjoy!