Lubuntu is a lightweight Ubuntu distribution for older PCs.
With the latest 18.10 release that has LXQt desktop, it makes it easy to change the location of personal files and folders.
Here is how :
From the start menu, go to Preferences > LXQt settings
Next, click on LXQt Configuration Center.
Then select Session Settings.
Over here, from the User Directories section, change the default location where various personal files are stored like Desktop, Downloads, Documents, Music and so on.
Click on the folder icon to point the default directory path to a new one.
Click Choose. Log out for the changes to take effect.
The new location should now be the default after logging back in.
All done.