reduce webplayer file size?

How can I reduce the file size of the webplayer file?
My current size is 48MB which takes very long to load so I try to find a way to reduce it. What can I do? So far I did the following:
- I set the textures to 512 instead of 1024. Is that enough or do I have to edit it in an external tool like Photoshop?
- I changed all wav files to mp3

Do I have to remove all unused assets or is this done automaticlly by Unity?

The build statistics shows the following:

Textures 66.7 mb 60.7%
Meshes 3.3 mb 3.0%
Animations 3.0 mb 2.7%
Sounds 2.1 kb 0.0%
Shaders 12.1 mb 11.0%
Other Assets 22.2 mb 20.2%
Levels 756.6 kb 0.7%
Scripts 1.1 mb 1.0%
Included DLLs 0.0 kb 0.0%
File headers 680.0 kb 0.6%
Complete size 109.8 mb 100.0%

I have 3 files with .asset endings from assets that I bought and use which are >10MB:
15.0 mb 13.7% Assets/MyBoughtAsset1/NavMesh.asset
12.9 mb 11.8% Assets/MyBoughtAsset1/New Terrain2.asset
12.1 mb 11.0% Resources/unity_builtin_extra
8.6 mb 7.8% Assets/MyBoughtAsset1/Demo/New Terrain.asset

When I remove the files everything isn't working anymore so I can't delete it. Is there any way to edit these files and reduce the size?

 

Sounds great. Do you have any link where it is described how to do that? I have some things like a cave system which can be loaded later and isn't needed in first place in my scene