The fresh air vents near your head at each seat can not be adjusted for temperature individually.  Cabin temperature is controlled. Just ask a Flight Attendant to warm it up as they have a control panel to adjust cabin temperature by zone. 

Most modern airliners use bleed air from the engines to power two Air Conditioning Packs which circulate cooled or heated air throughout the cabin. 

[Environmental control system (aircraft)][1]


B777 Air Systems Synoptic




[![enter image description here][2]][2]


  [1]: https://en.wikipedia.org/wiki/Environmental_control_system_(aircraft)
  [2]: https://i.sstatic.net/l3yUK.jpg