Ubuntu – I am trying to upgrade from ubuntu 18.10 to 19.04, and am unable to

I am trying to upgrade to Ubuntu 19.04 and am not able to. first, I tried this website: https://wiki.ubuntu.com/DiscoDingo/ReleaseNotes to try and find out if there was simply something that I had missed. I tried the same commands on this page multiple times, but to no avail, as it kept giving me this error: Checking for a new Ubuntu release
Please install all available updates for your release before upgrading.
then I tried going to One single command to update everything in Ubuntu? to see if there was some kind of command I was missing out on. I tried again and it still did not work. then I went to this website: https://www.liquidweb.com/kb/troubleshooting-please-install-available-updates-release-upgrading/ because it seems that others had the same problem. This website did not help either as it gave me the exact same error again. I have run all of my updates many times over, on multiple different wifi networks, and if it helps, my computer is a Ubuntu computer that was originally running Windows 10, but I deleted it because it did not have all of the features I wanted from my operating system. I now have new information and have found the problem, but I don't know how to solve it. my Simple direct media player package won't update, and I don't know why. I have now done some more testing and I found this:
The following packages have been kept back:
libsdl2-2.0-0 libsdl2-dev
I'm not sure why this is happening and it would be nice if someone could get back to me.
I hope that this question can be answered so that I and many others with the same problem can get help. with best regards, consume555.

it is now 19 days later and I have found the solution on my own. As it turns out, my sdl library was not updating, so I simply deleted it. I have learned that I should always check the terminal before seeking help. Thank you to everyone who provided input and I apologize for any inconvenience caused on my behalf.