As currently written, the only rule for creating a new infusion when you already have your maximum infusions is to automatically drop the oldest, so you can't simply choose to drop any infusion. This may change if/when the Artificer becomes official in a book release as it requires additional bookkeeping to track the order of infusions, and 5E generally frowns on such unnecessary complexity. In light of this, it is reasonable to house-rule that the artificer gets to choose which infusion would be dropped.
You can infuse more than one nonmagical object at the end of a long
rest; the maximum number of objects appears in the Infused Items
column of the Artificer table. You must touch each of the objects,
and each of your infusions can be in only one object at a time. If
you try to exceed your maximum number of infusions, the oldest
infusion immediately ends, and then the new infusion applies.
However, as written, you have one additional option - at the end of each long rest, you can create up to your full number of infusions. Assuming all items you have previously infused are available to you (as you can lend them to others so they could be any distance from you), you could simply re-infuse them in the order you desire, so that if you do need to infuse a new item (or change an infusion on an existing item) at a later date for some reason, you would have some control over which infusion would be dropped.
You could also swap infusions when you level to drop an existing infusion of your choice, but this doesn't seem terribly effective and is not likely to meet your needs.