I have 8.0-RELEASE-p4 + few ports installed. I wonder wheather I should update to 8.1.

1. How long is 8.0 supported?
2. How to update the system? I couldn't find anything about it in handbook.

**SOLUTION** (based on gvkv answer): 
I take the liberty of describing all steps I've done at the end: 

```
# STEP 1: Revert to GENERIC kernel
cd /tmp 
wget -r ftp://ftp.freebsd.org/pub/FreeBSD/releases/i386/8.0-RELEASE/kernels/
cd pub/FreeBSD/releases/i386/8.0-RELEASE/kernels/
sha256 generic.* install.sh | diff - CHECKSUM.SHA256
./install.sh GENERIC
nextboot -k GENERIC
# STEP 2: Upgrade - part 1
freebsd-update upgrade -r 8.1-RELEASE # Ignore kernel warning. Fix configuration
freebsd-update install
shutdown -r now
# STEP 3: Upgrade - part 2
nextboot -k GENERIC
freebsd-update install
shutdown -r now
# STEP 4: Upgrade - part 3
rm -rfv /usr/obj
portmaster -Raf # Rebuilds all packages. If you don't use portmaster use other tool or do it manually
cd /usr/src
make buildkernel KERNCONF=CUSTOM # Rebuild kernel
make installkernel KERNCONF=CUSTOM # Install kernel
shutdown -r now

```