Vuze is a BitTorrent client that is used for sharing files among peers. The completed parts of files that you are downloading through this client are automatically shared with other users; this is known as "seeding." There is no way to automatically turn off all seeding, but turning off seeding for any single file or for all files at once is a simple process.
Right-click on any single file you are currently seeding. Select "Stop" to cause that torrent to cease seeding. Select "Queue" to begin seeding that file again.
Select the "File" option located in the upper-left corner of the "Vuze" screen. Click on "Transfers."
Select "Stop All" to stop all torrents from seeding. Select "Start All" if you want to resume seeding all torrents.
It is considered poor form to stop seeding before you have at least seeded as much content as you have downloaded, so if the seeding is slowing down your computer, try leaving it on overnight to share as much as you've downloaded without effecting your time using the computer.