题主你好~
遇到这种对比，需要感知细小的区别，我们就尽可能地多去看他们各自的例子和英文直接的解释。
However: 1. (adv.) despite whatever amount or degress不管怎样，无论如何
e.g. However hungry I am, I never seem to be able to finish off a whole pizza.
2. (adv.) despite this 然而，但是
e.g. There may, however, be other reasons that we don't know about.
e.g. The garden is begining to look more respectable - there's lots more work to be done, however.
Instead: (adv.) in place of something or someone else. 作为替代
e.g. There's no coffee - would you like some tea instead?
e.g. How on earth could they knock down a lovely old building like that and put a car park there instead.
最后放两个终极对比例子。however和instead的区别？（这是例子的原回答出处）
He wants to get married before 26. However, he is still a bachelar after so many years waiting for his Princess.
He doesn't want to get married too early. Instead, he believes that owning his own house, which takes good years of effort, is a prerequisition of building up a family.
是不是感觉不一样。希望对你有帮助~
