I had a look at the specifactions for the se400. Under embroidery options it states speed control - so it must be in your user manual how to use it.
The only thing I found in my book had to do with the sewing speed. I did contact Brother and it turns out the SE400 is not designed to be slowed down. Kind of a bummer to say the least.
I have this machine and I love it, as cannot justify the complexity and cost of other machines. You cannot adjust speed for embroidery, but you can for winding bobbins. Have not used it other than for embroidery.
On your Esante (while in embroidery) select the button that looks like a paper. It is at the very top of the left of the screen. Go to page 3 (using the bottom right arrows) where you will find the Max Embroidery Speed. Adjust it with the -+
Sorry, I should have realized it was one with a different screen. It should be in your paper manual or you might find it using the book looking thing on your screen.
Hmmm...don't have either of those machines, but the speed control for my embroidery machine (BabyLock Ellisimo) is located in the settings pages...