How to update to WordPress 5.0 with old theme

Moved to Fixing WordPress, this is not an Everything else WordPress topic. Please post in the right place.

My site was initially created using WordPress 3.0 and picolight theme.

That’s a big jump. I’ll start with the easiest: you will need to get a new theme.

For upgrading to WordPress 5.0 please consider having a full file and database backup somewhere safe and then give this process a good read.

https://codex.www.ads-software.com/Upgrading_WordPress#Manual_Update

I don’t think he’s saying he’s still using WP 3.0, he says he, “installed every update of WordPress,” so I think he’s most likely successfully using the theme on WP 4.9.8.

If that’s the case, and he’s not getting any PHP errors or having any other issues, and if the Picolight theme doesn’t include any editor modifications he requires, it seems like he should be okay doing the automatic upgrade to WP 5.0, shouldn’t he?

linux4me2: you are correct. My site is on WP 4.9.8. All plugins are supported and have been identified to run on WP 5.0. The only issue is the now unsupported theme picolight. I am more than willing to change themes but am not clear the best way to do so without taking down my site in the process. For example:
(1) can I upload Twenty-nineteen or another supported theme and modify it on WP 4.9.8 then upgrade to WP 5.0, or
(2) can I upgrade to WP 5.0, continue to use the classic editor (which I assume means tinyMCE) and reasonably expect my current theme to continue to function correctly?

Number 2 would be the preferred choice for obvious reasons as it would allow me time to graduate to a more current theme and Gutenberg.

I’d recommend installing the Classic Editor plugin then the update to 5.0 and then activate the Classic Editor plugin as soon as the update completes.

I’d do a database optimization first then a good, full backup. I’d then install that Classic Editor plugin and do the update to 5.0.

Activate the Classic Editor and set the Classic as default editor.

If you don’t need to update right away then take your time when you do decide to do so.

I’ve only updated one of my sites so far and I chose a production site that might have been right difficult to fix had the update gone bad but it was smooth through the whole process.

That site is using the Tortuga theme with no problem. Twenty Seventeen also works with it just fine. My guess is the theme the OP mentioned should also work but that’s an educated guess at best.

@deaconchuck, I’d go with option 2, but I don’t think you need the Classic Editor plugin. When you update, all your current content will be in Classic Blocks, part of the Gutenberg editor, which you can continue to use for now. As long as your current theme still works, you can begin using Gutenberg to see how it goes. You can still use Classic Blocks in Gutenberg without using the Classic Editor plugin, if you desire, but why not give Gutenberg a chance? It has some really nice features and it works just fine, though it does take a little adjustment.

I’ve upgraded 30 sites so far, and only one of them is using a really old theme, but even it didn’t have any issues, and Gutenberg is working fine with the old theme as well. I’d give it a shot. : )

Both editors work with old and new themes.
You can easily preview new themes with your content through the Customizer. When you click on Change Theme button, it will show you the ones you have installed and also www.ads-software.com. Select a theme and it will install it, so that your content can be previewed. You can select one you like and Publish, and the theme change is done.
It is unrelated to updating to 5.0. You don’t have to update to the next version immediately. In fact, it’s a good idea to let the bugs settle out in the next minor release, and then update.

Thank you @linux4me2 and @joyously. I am reassured by your comments and suggestions. I will let you know how the update goes.

I didn’t see mention of it but I’d encourage you to do your updates/testing on a development site rather than enabling maintenance and updating on a live site. Testing is always a good thing. And of course, get a backup first.