One thing to do is to remove old kernels:

Do the following to keep just the last 2 kernels on your system, to keep /boot clean:

1. 1. Edit /etc/yum.conf and set the following parameter

      installonly_limit=2
      

      This will make your package manager keep just the 2 last kernels on your system (including the one that is running)

   2. Install yum-utils:

      yum install yum-utils
      

   3. Make an oldkernel cleanup:

      package-cleanup --oldkernels --count=2
      

      This will erase in a good fashion the old kernels, and, keep just the last 2 of them for the next upgrades.