Np I'll explain the different kind of updates:
Kit reworks are reworks of the champion abilities(these can include completely new spells,but sometimes they just change the effects of existing abilities)
Splash-art-update is simply what you call it when a champ gets a new splash art
Texture rebalance(sometimes called TR) are small updates to the textures of the champ to make them more fitting for the updated map(they are currently doing lots of these)
TU is a texture update for the champ(so no new animations or model,but a different look,like they did with singed)
MTU is a model-texture-update,this is a texture update with slight adjustments to the model,like making the champ a bit bigger,but keeping the model otherwise the same(examples are maokai,renekton and sona)
VU(or visual update) is a complete model update,its like riot deletes the old champ from the game and then makes him again.A VU comes with new textures,new spell effects,new voice-over,new animations and new model(examples are sivir,nasus,karthus and twitch)
A complete relaunch is when the champ gets a VU a kit rework and when his character and personality are changed drastically(the only examples would be Karma,Trundle and Sion)