Windows 10 May 2020 update is now available

How much data is required to download this update? Can I directly update my windows from updator? I want to update my windows which I am using for some time now. Please anyone can tell me some simple new changes in this update?

Mainly change: Headaches.

Suggestion: Wait 6-9 months

Installed new May 2020 update - after getting a notice that my system was not ready to install the update from Microsoft - and it worked fine for several days. Yesterday, my Outlook stopped responding when sending an email, then froze. When I tried to close the program it would not, even from the task manager. After than Windows stopped working. No programs would launch, both Microsoft and non-Microsoft programs.

Shut down and restarted my Surface Pro 3 and it started painfully slow and no programs or services would start. Tried troubleshooting several times to fix the problems and Windows 10 May 2020 just would not work. Managed to return the system to a previous build, 1909. Everything is now working fine, but I would like to know what may have caused this major issue.

Installed new May 2020 update - after getting a notice that my system was not ready to install the update from Microsoft - and it worked fine for several days. Yesterday, my Outlook stopped responding when sending an email, then froze. When I tried to close the program it would not, even from the task manager. After than Windows stopped working. No programs would launch, both Microsoft and non-Microsoft programs.

Shut down and restarted my Surface Pro 3 and it started painfully slow and no programs or services would start. Tried troubleshooting several times to fix the problems and Windows 10 May 2020 just would not work. Managed to return the system to a previous build, 1909. Everything is now working fine, but I would like to know what may have caused this major issue.

Well What may have caused this major issue is that, with respect you said it yourself , your computer wasn't ready to install the update , and you basically forced the update , there is a reason that Microsoft are staggering the update for 2004 , and that is to avoid a barrage of people complaining that their systems no longer work correctly , or that their piece of video editing software worked with previous version now doesn't work .  If you did not see Windows 10 updates when you clicked on check for updates then your system wasn't read for the May 2020 update.  And that alone should have told you best stay clear .

Working on updates is stuck at 90%. Been 5 hours now and hasn't changed from 90%. What do I do now? It says not to turn off the pc.

With respect , be patient let it run and under No circumstances turn off your machine   this update is around 4gb in size its big , so thats going to be alot of unpacking and installing in the background , walk away from the machine let it doe its thing , and as we say in the uk "a watched pot never boils"