Adjusting the length of the Elite Safety Tether is a very easy process, as shown in the 2 videos below:
Lengthening
To lengthen the tether, pull one end and as the excess starts to build up between the two cord blocks, take hold of one of the blocks and continue to pull.
Shortening
To shorten the tether, using both hands, pull the 2 cord blocks away from each other.