Should we? Yes. It makes a lot of things more simple. Physics, in metric, is wonderful. In imperial, a nightmare by comparison.
Do we need to? Not really.
Would it be easy or cheap to convert? No.
It would take quite a long time - as in, you have to actually start manufacturing everything in metric vice imperial. It would take over a decade.
Any company making anything would have to adjust their assembly lines and obtain entirely new molds.
The question being whether or not the convenience outweighs the cost. That's mostly what it is - convenience.
The thing that everyone seems to forget in the US customary/metric argument is that most countries are hybrid. For instance, the UK still uses pint glasses and does weight in stone, despite being a "metric" country. And the US sells some drinks in liters, holds races in meters, and trades stocks in decimals, despite being a "not metric" country. We just lean a little further away from metric than most other countries.
It'd be easiest if they started by teaching it in schools. It'd be simpler for kids to learn, too, being based on a small, round number like 10, as opposed to the whimsy of imperial. Sure it would take a bit before actual change began to occur, but change doesn't happen overnight, especially where most of the adult population is concerned.
The English system has advantages the Metric System does not. For example, it is inherently more native in Binary and Hexadecimal. The English system is also stronger in fractions than decimals. How children develop in these two systems intellectually is different, but those differences are collectively complimentary. Having some scientists better at fractions and intuitive understanding of values like 32x32=1024 and knowing what 1/64 is - this is an advantage. Being able to convert rapidly between the two systems also helps these kids understand natively different mathematical and linguistic paradigms by analogy.
I've heard there are Sanskrit rhymes that act as mathematical operators, that there are Hanzi for derivatives and integrals; that Hebrew and Greek are both numbers and letters. I think if anything, children should learn more systems, not less.
I can use either, so it doesn't really matter to me, but you are not going to convince a carpenter that has been building houses for 20 years that he needs to stop using feet and inches and use meters and centimeters, it's just not going to happen.