Unfortunately, there isn't a manual for the KickStart software, currently.
We have some helpful videos developed for KickStart on our support YouTube channel:
https://www.youtube.com/user/TektronixSupport/search?query=kickstart
Some of these videos are using older versions of KickStart, which will not show all enhancements currently included in this growing software solution, but will give you a good starting point.
Sample Rate in DC measurement on most instrumentation, including our DMMs, is governed by a multitude of settings (NPLC, filters, delays, etc), rather than a direct 'sample rate' parameter.
The DC functions prioritize accuracy and speed/rate are a secondary aspect.
Speed/rate will need to be optimized based on those accuracy-first parameters.
If you want the control of sample rate, primarily, I recommend using the Digitize function.
This will provide a direct sample rate field that you can utilize.
Digitize Voltage and Digitize Current prioritize the sample rate parameter.