Learn to do this yourself. There are helpful how-to videos on youtube, if you want to watch someone else demonstrate a string change.
There's an ongoing debate about whether to remove all the strings at once. I've usually remove one string, and replace the one in that position before going to the next one.
Now, I'm mentioning this since I removed all four strings (before replacing them) on a bass today, and the neck went into a back bow position. It took longer than usual before it settled down with the new strings, and much more tuning time was required as compared to one-at-a-time.
It's not that anything was damaged, it just took much longer for the bass to tune than usual.
“To play without passion is inexcusable!” ― Ludwig van Beethoven