Can Google Pixel C tablet Android OS update every version? If there releases a new android version, can google pixel c tablet update that soon by user himself from system control tool?

Is it the same as iOS update?
In practice an Android device can only be updated by an update provided by the device manufacturer. This is not the same as an iOS update.

An update provided by the manufacturer contains a great deal of device specific code and data which the android version provided by Google does not. Each new version of Android has minimum hardware requirements which older hardware may not meet. Manufacturers receive the update in source form and add the code needed to interface with their hardware. They may also need to customize the Android code according to their own requirements.

In some cases it may be possible to update from other than the manufacturers update but this is for experts only and would require a great deal of time and effort.

This is one of the unfortunate realities of the Android market. Manufacturers would much prefer to sell you a new device than update your old one.