If I compile my Bitcoin core wallet, does this means I'm supporting this UASF, and if I don't compile it I don't support it?
What would happen if I compile my wallet and then it isn't accepted by majority? Do i need to ''uncompile'' it?
Compiling is the process of building an executable from source code. It has nothing to do with supporting or not supporting a proposal in Bitcoin. You can compile a version of Bitcoin Core which has BIP 148 support. You can also compile a version of Bitcoin Core which does not. You can also just download and install the pre-compiled versions of those software.
Bitcoin Core does not support BIP 148. This is simply a fork of Bitcoin Core maintained by supporters of BIP 148. It is frequently updated with the latest changes from Core (as new releases are made) and a small patchset with the BIP 148 stuff is applied on top.
Does all the other wallets need this change (update, compilation) too? If I have wallet on android do i only need to update it or what?
Any consensus rule change requires that all software must have their source code updated, recompiled, and released as a new version (it must have proper versioning, otherwise users will be confused). This is usually done on the developer's side as they will publish pre-compiled binaries for you to download and install.