Hello everyone,
I hope this will be helpful for those who doesnt bought every track and every car who wants to save disk space with Steam version of iRacing.
The content I own is only 16gb - so it makes sense.
So this is solution and looks like it works with me.

1) So first of all download game in Steam - it will take around 82 gb of disk space.
Btw steam downloads all content including locked tracks and cars.
Launch iRacing UI then close it.

2) Next step you go and delete both "cars" and "tracks" folder containg all stuff on you disk.

3) Next step you go to iRacing Member website with ur account and click on button "Manage software updates and downloads". This can be found on left side on grey bar with circle icon.
A new dialog window appears.

4) Next step you choose to download all available stuff which is free or which u already bought.
Be careful and leave "optional" content, dont choose it.( optional content mostly take disk space).

5) Next step - open iRacing Updater (can be found in iRacing folder on your disk in folder "updater") and click update.
It will install download all content you chosed before and install it.
You will be able already see the size of update which is important.

6) Once update is finished, launch iRacing and enjoy playing with content you have.

If you will buy later any track and cars, I bilieve you will have to return to part 3 and choose / check new added content and then update again.

Hope this helps someone!