'incorrect user name and password'

I am a beginner with windows 10.
When I log in I now get 'incorrect user name and password' and I see I have now got two User Accounts in my own name. How do I get rid of the wrong one? (I'm sure this has been asked many times but I couldn't find it in FAQs). Since it appeared my Pc is very slow to come to life - I have time to make a cup of tea before the desktop appears.

I'm out of my depth here.
I am 77 and until this update, have been weaned on XL so this has been a HUGE learning curve. This laptop I have now (a Toshiba Satellite C850D) isn't a touch screen, but I got on OK with windows 8.1 on it.
It updated itself (I may have pressed something) to Windows 10 and I've had nothing but trouble since, so I took it back to the shop to check if I could reinstall windows 8, or if it had a virus or something. A young wizkid was appalled by my lack of security and sold me Kaspersky, then he changed the loh on details and showed me what I had to do at the new login screen.
I have to enter Ctrl/Alt/Del at startup, then he put in my details for logging in - they were
1, my user name (my christian name) and microsoft email address and password
2, my second user name (my full name) and yahoo email address and password
3, my Admin and password

That was all quite simple.

Then with the last update from windows, the 'incorrect user name ... etc came up each time I logged on, and in inspecting the screen I saw another (4th) log on name which was a corruption of my microsoft name and 000.
Its that log on name and password I need to delete - without deleting the first three options.

I'm a bit long in the tooth to start messing with registrys and such, the warnings that come up with netplwiz scare me rigid. I quite like having the option of two email addys to use for logging on. I would just like to delete (or hide) the fourth option without a major upheaval if possible.
I was advised to change the rogue account to my usual one ..... so now they both look the same but the rogue one doesn't log on - its impossible to recognise which one is right.
I don't want to lose the option of a backup logon email address, or my ability to logon as admin.

Oh dear - its back again today. (my screen in 'accounts' setting doesn't look at all like those shown in any of the suggested fixes, so maybe I'm doing something wrong like not clicking a hard to see 'Apply' or something).
I tried a long convoluted 'fix' from Cortana some days ago ..... but it came back again and again.
I guess I can live with it, its annoying more than anything.
Not impressed with windows 10 yet though!

no worries - I'll live with it. Every time I try something I seem to make things worse, so I'm stopping while I can still get into the darn thing. I'll take the pc back to the shop and get them to fix it if I can't manage - after all it is just a matter of going back and choosing the correct user account instead of the rogue one.
Now I find the typing jumps around the text and th appearanc of the text onscreen is slow so that leters are missed altogether and I have to keep gong back and repairing things.
I've just made things worse.