Forwards/backwards
There is a handle under both front seats. This allows you to move the seat forward/backward.
Backrest
On the side, you will also find the lever to adjust the backrest.
Up/down
The up/down control is next to the seat. It works with a spring, so not like most chairs. First, without sitting on it, you have to make the chair jump to the highest position by pulling up the lever. Then you have to sit on it and raise the lever again to adjust the seat to the desired height.
Are you comfortable yet?