If you have not used a proxy you can use the "Vote For Witness" under the the black bars by your icon if you are using steemit, which is this link https://steemit.com/~witnesses but it will/should always be available on the menu, I think it is in numerical order of witness, but am not sure. Also if you use @steemchillers steemworld.org you can get the witness list at the bottom under his tools tab.