Hey, quick question. If I upload my personal best but then I get a better one and upload that one, does it replace on the leaderboard with the updated one?
To be more precise: When you get better runs, your previous runs are marked as obsolete, but are not deleted from the leaderboard. You can see obsolete runs in a leaderboard with the relevant filter, or in a user profile page with the "show obsolete runs" switch.
And while it is ultimately your decision, most runners prefer to see as many runs of their games documented as possible. So if you've submitted a run and beat it before it's verified, leave the old run in there and submit your new one too! Site guidelines discourage moderators from rejecting submissions simply because they are obsoleted by newer runs. If the category is one that requires high scrutiny to verify (a glitchless category, to ensure you don't do glitches, is probably the best example), maybe don't drown moderators in submissions (though ultimately, verifying runs is what they volunteered to do, so it wouldn't be wrong on your end if you did). If it's a more straightforward any% run where all that needs to be verified is timing, I say go nuts.