Headset Length

[Bianchi]

How can increase my steerer tube length?

 

[Black Dog]

You can get a headset with a shorter stack height or buy a new fork with a longer steerer tube. I assume that you are talking about a threadless head set.

 

[Notso Swift]

And if the reason you wish to do it is to adjust the handle bars you can change the stem
Multiple angles are available even though most are -/+ 4 to 8, (flippable) you can get them from 0 to about 12, after that you can get adjustable ones