The template I’m using has a basic vertical drop-down menu, but as stated, I would prefer it to drop down vertically.
It drops down vertically but you want it to drop down vertically? I’m confused.
I assume from your title that this is actually a horizontal menu.
The first thing you have to establish is “will the template let you do this?”.
If so, then we can proceed.
To do that we need to see the current HMTL & CSS, ideally in a reduced Codepen.io example so we can offer advice on what, if anything, can be done.