Kernels are at the heart of every operating system. The Linux kernel can be customized in a wide variety of ways. Two methods are based on loadable modules and changes to runtime parameters in the /proc directory.
The easiest way to update a kernel is to install (and not upgrade) from a Red Hat RPM, or use the yum command to install from your assigned repository. When you do, it automatically updates your boot loader files as needed.
Alternatively, the kernel can be optimized for your particular installation and hardware, and you have detailed control over its configuration. Once customized, it's a lot easier than it used to be to make a modular kernel; the make rpm command is all you need to create a customized kernel RPM. It's not perfect, as you still need to create your own initial RAM disk and corresponding stanza in your GRUB configuration file.
While it's best to configure RAID and LVM during the installation process, you may also need to do so after installation. RHEL supports a variety of software RAID types, including RAID 0, RAID 1, RAID 5, and RAID 6. LVM makes it easier to expand the size allocated to an existing filesystem; RHEL includes the GUI LVM tool to help.