How do I level up stats instead of skills in DotA 2?

I've seen a few guides for various heroes (mainly on DotA Fire) that advise leveling stats instead of skills at level 15, then from 17 to 25 (when skills have been maxed). How do I do this? (What do I need to do after clicking on the gold 'level up' button?)

Solution 1:

When you level up, a gold "Level Up" button will appear right above your character's portrait.
Upon clicking it, a gold/yellow border will circle your stats bar and any abilities you are able to upgrade.

To level up your stats instead of skills, click the stats box and 2 extra points (per time you level up your stats instead of abilities) will be allocated to each attribute. Alternatively, you can press Ctrl + U when the gold button flashes (instead of pressing Ctrl + W/A/S/D which is the hotkey to level up your skills).

As a sidenote, leveling stats is really good and often overlooked in the "guides" that you can use in-game. Stats is especially good when learning the game, so you can focus on the action with higher damage when it happens and not your 6 different 1-6 and W/A/S/D hotkeys/abilities/item abilities.