How do I use a 3D model mod?

[Koffee]

Found a mod called "Miles' Mildly Improved Model Pack" and I'm trying to get it to work, dunno how to though. Do I need to remove the Sonic model files and replace them with the new Sonic model add-on?

 

[DylanDude]

Here is a tutorial:

Model - SRB2 Wiki

 

[nikoberry]

Here is a tutorial:

Model - SRB2 Wiki

Note, the Wiki does not mention this, but due to Linux being case sensitive (unlike Windows), you might have to rename the files.
Character names usually are completely capitalized and "_blend" is always lowercase.
(for reference, BLEND is completely capitalized here so the model remained pink)