open the "packages/base/models/ogro/md2.cfg" file.

Where it says "mdlscale" change the number to 100.

As for the skin, if there's any textures that look like the ogro skin, rename them to "skin.jpg". The yelow texture is probably the "texture not found" texture.

It seems like you've deleted or modified the configuration file of the ogro-model and it's skin.
I guess the white letters are saying "texture error"?
You can do 2 things now;
- reinstall sauerbraten or try to obtain the original skin and it's configuration-file on another way.
- Click on this link to obtain the whole ogro model, but never do such thing again without being sure you still have a backup of the original file. Use your brains when modding stuff.