That seems needlessly complicated. Why not just give the player the ability to increase the stats on the page where the training was done?
That said, using an item, you would still create the STAT variable, the "Level Up" item, and the "Level Up" page. You would go to the global page script and input:
IF %STAT = 0 THEN $ITEMSTATE01 := 0
IF %STAT > 0 THEN $ITEMSTATE01 := 1
This assumes that the ID of your "level up" item is 01. If it's 02, you will use $ITEMSTATE02, for instance.
On the "Level Up" page, you will use on-page variable code to display the user's stats (the article explains how) and create a link for each attribute the character can increase, as well as a "go back" link. The attribute links should only appear if the STAT variable is greater than 0 and, when clicked, they should decrease STAT by one and increase their respective attribute by one.