mhwd supports installing multiple kernels. Manjaro includes kernel 3.4-series as default, kernel 3.2-series as longterm-kernel and kernel 3.5-series as testing-kernel.
USAGE: /usr/sbin/mhwd-kernel current-kernel new-kernel (uninstall current) yes/no
I assume you have linux34 installed and you want to try out linux35. Maybe a newer kernel might improve your system. Install kernel 3.5-series with:
sudo mhwd-kernel linux34 linux35 no
mhwd will install linux35-package and it’s extramodules if you have any installed for linux34.
To remove it you can use pacman:
sudo pacman -R linux35 linux35-headers linux35-extramodules