In short, if you want to preload The Ascent, you will first need to pre-order the game on your desired platfrom. Once purchased, you will need to start a download for it via your platform. On consoles, this process will be simple and most likely down automatically for you once you bought the game.
If not, you can download it by finding it in your library and clicking download. Meanwhile, the process doesn't change much for PC users. To preload the game, you will need to find it under your game's library and click download.
Related: How long to beat The Ascent?
For Steam users, you will get an option to do this right after purchasing the game, and it may also refer to the download as preload instead. That said, do all of this, and you will be able to preload The Ascent and have it ready for its release date this week.
How big is The Ascent's download size?
For all platforms, the download size clocks in around 17 GBs in size, so depending on your download speed, you should be able to load in pretty fast.
When will The Ascent be playable?
In short, there is no date at the time of writing regarding what time the game will unlock and release at.
For more on The Ascent, we highly recommend checking out both How long to beat The Ascent? and Will the Ascent be on the Xbox Game Pass at launch?