Assume that:
I opened card A a long time ago and card B recently (different institutions).
I have a very high credit limit on credit card A and a very low one on credit card B.
I do not need the former but I do need the latter. (When I tried to go over my limit, B was declined.)
I have a decent credit score, make payments on time, and don't have credit problems in general.
So I want to raise my limit on B, but to ensure it will be approved, I have no idea whether it's better to lower my limit on A first since my current combined credit line might be too high, or whether I should avoid that since my utilization will rise. I'm also not sure if the fact that I opened B recently affects this.
In what cases should I lower my credit limit on A before raising it on B? In particular:
(When) would it help with whether B will get approved?
(When) would it help reduce the hit to my credit score (since B would result in a hard pull)?
And if lowering A affects the effects of raising B, around how long should I wait between the two?