Science does support atheism. Atheism is the absence of belief in theistic gods, or if you'd rather, the assumption that such gods don't exist. Everything we know from science shows us a universe where gods are unnecessary and unlikely. It does not disprove a theistic god, but it does support the nonexistence of one.
In science you start with a hypothesis, and then test it to see whether it holds up. If it doesn't hold up, you either discard it or tweak it and then retest. If it really isn't supported at all, you, for all intents and purposes, assume it's not the case. For instance, you could have the hypothesis "People with more than 10 toes are faster than the average human". You could then test it by timing people with more than 10 toes and comparing to the average human. If tests didn't result in support for the hypothesis, it would be dismissed and assuming not to be true.
With God, of course, we can't test the general hypothesis "God exists". We'd have to narrow it down. Atheists generally really only fully dismiss theistic gods, which have certain traits we can actually test. Once we test them and find no evidence to support them, we can safely assume the claims about that god, and therefore its existence, aren't true, even if we can't rule it out with 100% certainty.