A quick foreword, I'm focusing these changes to be more combo-focused. I am a combo player, so some of these changes you might want to take with a grain of salt. That said, I'll try to note changes that are just for a stronger combo finish and what changes are for higher overall consistency.
Why you should cut these cards:
The biggest and most overarching problem with precon decks is that they aren't focused and tend to have several themes going on all at once. Often, this leads to turns that aren't well-aligned. Most of the cards that I'm suggesting on cutting just don't follow a consistent theme. There are also a lot of cards that I cut because they will lead to a more "stompy" wincon. If that's something that you're interested, we can double-back a figure that stuff out.
Amoung these "stompy" cards are things like Crackling Drake, Talrand, Sky Summoner, and Murmuring Mystic. I think these could make for a fun deck, but that can be worked towards later.
Another large group of cards that I recommend changing are the instants. Most of these are just don't do enough for the amount of mana they cost. Let's take Temur Charm as an example. Firstly, I love modal spells. They can do a lot, but are often inefficent for their cost. The three-color charms are probably the worst offenders of this. The first mode on Temur Charm might take down a creature. The second might counter a spell (but likely won't), and the third will clear out very few blockers. All and all, not very good. I did include all the two-color charms in these colors, but I'll talk about those later.
Why you should add what these cards:
I'll break these recommendations down into a few categories, ramp, copiablity/value, and combo lines.
In all of three-color decks, I run all the signets and talismans that I can. Two-mana mana rocks are the prime rate you should be looking for. They will help you power out an early Kalamax or helpful spell. Because of this, I rarely run more than 33 lands. That's a number that I've had great success with, but I usually play in a more combo-centric way I want to be drawing efficient spell that will help propel me to my win cons. If you want to run more lands, that's understandable.
One of the major upgrades you can make is adding more copy spells and spells that do well when copied. Manamorphose is a prime example of this. Normally, its a "free" spell, something that costs mana but gives it right back and it replaces itself. That's not a bad deal, but it isn't a game-changer in EDH. With Kalamax out, MM gives you an extra two mana and draws you another card, which can really help you out.
Lastly, I have two major combo lines, one of which ends the game. Let's start with the value line. With Underworld Breach and Frantic Search and/or Windfall, you can effectively dig through your whole deck. With just Windfall, you will be losing three mana each time, but it should also help stock your graveyard. Eventually, you'll get to FS. With this, you're netting zero mana and losing a card. The other major combo line is Ral, Storm Conduit and something like Fury Storm. You already had Ral in your sideboard, so I assume you know how that combo works