How do I know what type I have ? Is the any standard size to a modern BB. I do have external BB I think. But I do not know what size it is? There BB looks to be average size but I do not know if it is oversized, appears threaded I guess. Are they serviceable or just replace the entire BB unit. I am old schooler so the older types I am good with.
I need to replace chainrings and figured BB would need new bearings or to be replaced as well.
Thanks.

Start with crankset brand, then model, and/or pictures. Bottom brackets are one of the most varied parts on a bicycle.

New stuff, I don't know either. I usually swing by my local bike mechanic & ask, for stuff like this. Maybe someone will pipe up, here.

many people post pictures to get answers.

Quote the website for the brand and model of bike you bought, if you can't just go to a bike shop and ask.

There are multiple standards, both for the frame's bottom bracket shell and for the crankset/spindle. It's sort of a case where "the more things change, the more they stay the same". In the old days, your frame could be English/Italian/French threaded, or even Raleigh's proprietary threading. Today it's English threaded, BB30, etc. Back in the day, you needed to know if your crank needed an ISO or JIS spindle and what length. Today, it's the spindle diameter or type like Hollowtech II (24 mm) or BB30 (30 mm).

You may be able to visually ID your bottom bracket from markings on it; otherwise you'll need to cross-reference your bike frame and crankset to look up the specifics. We can often help with that if you were to post the brand/model/year of your bike and the brand/model of crankset, or if you post pictures.

Most current bottom bracket designs have sealed cartridge bearings that aren't meant to be serviceable.

If the bottom bracket spins smoothly, there's no need to disassemble and service/replace. Just keep on riding 'til it gives you trouble, then replace it.

Grand Cru Threadless Bottom Bracket

This link is for a BB that is adaptable to various road bike BB shells. If I needed a new BB for my old Raleigh, this is where I would go.

While the VO threadless bottom bracket does come in handy sometimes, it most likely wouldn't be useful for the original poster. He mentions a "modern" bike with what he thinks might be an external bearing bottom bracket. The VO threadless bottom bracket might not fit the bottom bracket shell, depending on what type it is. And being a square taper bottom bracket, it almost certainly won't fit his crankset.

Maybe this will help: Whether or not the bearings need to be replaced does not depend on the desire to change chainrings.

If you want to know what BB you have, look closely at it, write down any and all character strings printed or stamped on it, put those character strings into something called an "internet search engine", compare the results with what you have paying particular attention to the pictures, then go shopping. You could also post in the Personal Research and Shopping Service forum. HTH.