Agnosticism relates to knowledge, not belief. Knowledge being a sub-set of belief.
When I was a Catholic, I was an agnostic Catholic. I believed God existed (because I had been taught so from my earliest memories), but I didn't claim to have actual knowledge of whether a God existed or did not.
When I went back and has a proper examination of my religious beliefs in my late 20s and early 30s, I realised that I had no justification for what I believed (quite a shock at the time). So I abandoned that belief.
It still doesn't mean I assert no God exists. From my perspective, it could well do. It's just that I don't think anyone has presented me with sufficient evidence to accept a claim that it does.
(As an aside, I enjoy these sorts of discussions with my family and have been fascinated by the changes in their beliefs over the last decade or so. My sister, after lots of back and forth on this, would be classed as an agnostic Catholic. My brother has become an anti-theist - that is, he is convinced that no deities exist. My mother has gone from being very laissez faire Catholic to ignostic - after research and reading, she say the atheist/theist dichotomy is meaningless, as no concept of a deity presented to her makes any coherent sense. My father is probably closest to myself in his beliefs - in that he shed his belief that the Judeo-Christian God exists but doesn't positively claim that it does not exist.)
