The options you are given at boot are just different kernels. There are no 'restore points' with Linux.
If you want to get rid of the unused kernels, you can uninstall them with 'rpm -e <kernel-<version>>'
To find which kernels are installed, you can do:
rpm -qa | grep kernel-
This will give you a list of the kernels installed. For example, on my machine I have:
[0 dave@cronus ~]$ rpm -qa | grep kernel-
so I would do:
rpm -e kernel-220.127.116.11cronus-6
to get rid of the old kernel.
Be careful, though. If you make a mess here, you could end up with a non-bootable Linux system. It's unlikely, though, as RPM will not uninstall all the kernels, unless you specifically tell it to. You'll only be saving space on the /boot partition, though, so it won't make any difference to the amount of space you have to keep normal files in /home/<user>.
If you install something you don't want, just uninstall it, using 'rpm -e <package>', or use the GUI package manager (pup) from the menu.
There's no need for anti-virus software, because there simply aren't any notable virii on Linux.
Defragmenting isn't necessary on Linux, because the ext3 filesystem you will be using on Fedora doesn't fragment the way Windows filesystems do (until the disk gets above around 90% full, anyway).
To be honest, if you're using your machine as a desktop/workstation, there's no need for housekeeping, except for running 'yum update' every week or so. Unix/Linux tends to be a 'set and forget' affair - if it's working, it's all good. Don't worry about it.