Installing new mesh/autogen

I have a question regarding a new mesh installation. I'm new to flight simming although I've made some successful additions of mesh, aircraft etc. in FS9. I'm no computer whiz but after 10 years usually manage to fumble my way through things.My question is this. I've downloaded the free Asia/Spring mesh from FSSceene and when I began replacing files in scenryworldtexture I found the first two files I was replacing were larger (by a factor of two) than what I was adding. That caused me to pause, have a think and write this post. I have added a small area (Tibet) of new texture before and am wondering if I might be replacing those files with something not as good or conflicting.I thought of just replacing the files that are smaller but wonder if I might end up with a checkerboard of textures.Any guidance on this would be appreciated. If someone knows of a discussion or article that might help me just point me in that direction.TIA