The Alliance does not have a ranking-up system like the other two superpowers do. You support the Alliance because you agree with their philosophy, lifestyle and colour aesthetic, not because they have ranks and titles.
The Alliance does have a Reputation score, as do the other three superpowers, which is your reputation with the superpower. To boost this, go bounty-hunting. Handing over about 500,000 credits worth of generic Alliance bounties should make you Allied with them.
Assuming your question is actually about attaining the next rank up once you hit 100% on the rank score, you need to then do an "ascension mission". Find a minor faction aligned with the Federation, and there might (not "will", there won't always be an ascension mission present) be a mission offered with "Federal Navy" in the mission title. It will also include the next rank in amongst the mission rewards. Successfully complete that mission, and you will have attained the next rank.
Any "rank points" earned while sitting at 100% are not lost, they get banked and put towards earning the next rank.