The sentence structure of the following sentence In the following sentence:


  此前的摩拜单车以橙色为主色调，此次发布的新车型改用了白色。另外，在零部件的更换以及坚固性上也有所优化。


In the sentence bold above, if I understand it correctly, the meaning is something like the follows:


  The parts have been upgraded to more robust ones and to some extent optimized.


However, I don't understand the grammartical structure of the bold part. Specifically, what I don't understand are:


What does 零部件 (parts) modify via 的? Is there something omitted here? For me 更换 seems to be a verb so it is awkward that 零部件的 modify it.
以及 means "as well as", and works as a conjugate. But what does it concatenate here with what? 
How does 上 work here?
零部件的更换
零部件=(mechanical, electrical, etc) part; 更换 = replace/replacement (it can be a noun), so 零部件的更换 = replacement of parts
坚固性= ruggedness
Have you noticed the structure 在...上 used here? It means &quot;with respect to; regarding; in terms of&quot;, so the sentence may be split into (I think 零部件的 modifies 更换以及坚固性 here):

在[零部件的(更换/以及/坚固性)]上也有所优化
There are some optimizations regarding the replacement and ruggedness of parts.