Are the locations picked based on some particular vote in Esperantujo or are they picked by the same committee that makes decisions on changes made to the language? Or is it based on cost, etc...
The board of the Universala Esperanto-Asocio, UEA, is the specific organization that decides where the congress takes place. They make the decision based on proposals by local/national organizations. You can read more about the decision-making process in an article on Libera Folio: http://www.liberafolio.org/2014/bonaero5
"Fine de la kunsido estis publikigita ankaŭ la estrara decido pri la Universala Kongreso en 2016 kiu estis farita en merkredo. La kongreso en 2016 okazos en Nitra, Slovakio."
About the UK and the IJK (the international youth congress): "Neniam UEA aŭ TEJO decidas proprainiciate organizi UK-on aŭ IJK-on en iu loko. Nur la lokanoj unue faras la peton kaj surbaze de tiu peto la respondeculoj de UEA aŭ IJK unue esploru la eblecon." (http://www.liberafolio.org/Members/chiam.pozitiva/afriko-ne-estu-escepto)
This is decided by UEA (the World Esperanto Association), but local Esperantists have to make a proposal. For example, this year's congress took place in Nitra, Slovakia, but Lisbon was also a candidate. People from UEA visited both cities and their proposed congress venues two years ago before making a decision. I am not sure if there is a vote or if a small committee or one persone takes the final decision.
UEA has no direct institutional links to Akademio de Esperanto, which is the institution that you probably intended with the phrase "the same committee that makes decisions on changes made to the language".