Try opening them in the editor. I'm hoping at least one of them is unprotected.
I don't really have a tutorial handy, but what I can tell you to watch out for would be overlaps. If you want to completely redo the four races, then I guess it'll be fine. but if you intend to add new races, avoid having units that use the same abilties or are just different looking but have the same stats/abilities/etc. Try to have a mechanic that's unique to your custom race (for example, the Undead can summon/unsummon buildings and must always build on blight. The Night Elves will only regenerate at night. That kind of thing).
As far as units go, 12 should be a stable number to aim for if you want to remain in the wc3 mold. I suggest copy/pasting units from existing race and modifying their stats and abilities. The same deal goes for buildings, but depending of how many upgrades and stuff you'll have the number may vary (point in case: humans have more buildings that orcs because of all the towers they can make). Consider giving your farm-type building (something that gives food) a unique mechanic to make it more interesting. As an example, the Orc Burrow can be garrisonned to attack nearby enemies, the Moon Wells can heal, and the Ziggurat can be upgraded into towers.
If you want to follow the warcraft 3 style closely, you'll want at least 2 caster types in your army. Eg: Priest and Sorceress, Druid of the Claw/Talon, Banshee and Necromancer. The Orc are a bit special in that Frozen Throne added a third caster unit, so don't be afraid to experiment.
All that being said, don't be afraid to think outside the box! Maybe your race starts with maximum food and doesn't have to worry about supply, but everything they can build is expensive to balance them out. Or maybe all the units of that race is trained from one single structure, like the Zerg in Starcraft.
PS: turn off Brush List in your editor (Window > Brush List. Untick it). It'll remove the lag from creating and editing units in the data editor.
PS2: one thing you should keep in mind while editing - almost every unit has an ability of some description, or fulfills a certain role. The Footman can learn Defend, the Knight is a tanky bastard, the Headhunter can upgrade to Berserkers, who have Berserk. You're not required to give every unit an ability, but most should have at least one.