It is a bit different. You cannot
just switch classes.
LaTeX itself (or to be more precise TeX) is like LEGO, stacking blocks/bricks/boxes. The standard classes provide a limited set of extra handy bricks to play with. Many extensions have been made for the LEGO kit.
memoir and KOMA-script (bundle) provide classes that are far more complex than that basic kit from before. Imagine it as the Star Wars LEGO kit, and the Harry Potter LEGO kit. It will be o surprise, that parts from a spaceship look weird in a magical setting. Maybe the bricks won't even fit.
For a standard class geometry is the way to go to set up page size and margins. But not for memoir. Memoir has its own internal set of macros to do that. KOMA is a whole bundle and has its very own package to do the same task. Luckily, the geometry package can be used with all sets of bricks.
Package tocbibind is great for the standard classes, but it destroys functionality of both KOMA-script and memoir. Both have their own way of doing the very same task.
fancyheadr is great for the standard classes, but onnce again, memoir and KOMA-script have their own way of doing stuff.
You have to commit to one of them and stick to it.
And now to really frustrate you, most journal classes are based on that very limited and basic LEGO kit called standard. And
each journal adds new bricks. Why not? There is no need to customize anything. It (the layout and fuctionality) needs to be fixed.
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To put it another way: TeX provides everything to biuld some tools. Standard LaTeX classes provide a basic set of tools, including 7 different screw drivers. KOMA-script and memoir are like an electric more powerful screwdriver, different bits you can choose from (flat, phillips head, torx in different sizes). But if one bit is missing, you are screwed.
Journal classes (of course not all) are like a hammer fixed with gaffa tape.
EDIT: Just look
here. What Stefan posted is suitable for all classes. What i suggested is only valid for that template with that class. Both KOMA and memoir have a similar, but different way of doing the same task.
The smart way: Calm down and take a deep breath, read posts and provided links attentively, try to understand and ask if necessary.