missing guest account when upgrading from windows 8 to 10.
'Local Users and Groups' option not available 
Probably available on the Pro version of W10.
Probably available on the Pro version of W10.
read it all before you try anything 
if its just the folder(s) where the info was stored then a simpler option would be
open the file folder icon on the task bar (or desktop) click on "this computer" click on the "c" drive, open the "users" folder left click once on "guest" folder then right click selected properties, security advanced and grant your account full control over that folder (assuming your the pc administrator)
this should then give you the ability to open all the folders and access any information you had stored in there.
top tip for the future, store anything vital on cd/dvd external disc and a thumbdrive (use them all you cannot have to much duplication for important files) and definitely don't leave them on a hard drive that your doing an in place upgrade on /
if taking ownership (and applying to all child items) doesn't work from normal logon then hit windows key +r type in "msconfig" and hit enter, in the popup open the "boot" tab check the "safe boot" box and restart the system (it will now start in safe mode) you should now be able ot use the take ownership / file security change options to gain access to the stuff you require.
in future store this info on a thumbdrive or in a onedrive folder you can access from your mobile or any pc you log into, do not use a guest account as anyone can gain access to it wither you wish them to or not /
actually try this before creating a guest account which might well delete the existing user folder or render it inaccessible,
hit the notifications icon in the task box, hit the settings button, in the address bar click on the words "control panel" if you know which bit account management comes under then click on it otherwise change the drop down icon in the right hand side of the window to small /large icons then click on users, from there guest account management should be easy enough to get to
if its just the folder(s) where the info was stored then a simpler option would be
open the file folder icon on the task bar (or desktop) click on "this computer" click on the "c" drive, open the "users" folder left click once on "guest" folder then right click selected properties, security advanced and grant your account full control over that folder (assuming your the pc administrator)
this should then give you the ability to open all the folders and access any information you had stored in there.
top tip for the future, store anything vital on cd/dvd external disc and a thumbdrive (use them all you cannot have to much duplication for important files) and definitely don't leave them on a hard drive that your doing an in place upgrade on /
if taking ownership (and applying to all child items) doesn't work from normal logon then hit windows key +r type in "msconfig" and hit enter, in the popup open the "boot" tab check the "safe boot" box and restart the system (it will now start in safe mode) you should now be able ot use the take ownership / file security change options to gain access to the stuff you require.
in future store this info on a thumbdrive or in a onedrive folder you can access from your mobile or any pc you log into, do not use a guest account as anyone can gain access to it wither you wish them to or not /
actually try this before creating a guest account which might well delete the existing user folder or render it inaccessible,
hit the notifications icon in the task box, hit the settings button, in the address bar click on the words "control panel" if you know which bit account management comes under then click on it otherwise change the drop down icon in the right hand side of the window to small /large icons then click on users, from there guest account management should be easy enough to get to