Can't update my ubuntu kernel

after I updated my ubuntu to 18.0.4 （Welcome to Ubuntu 18.04.6 LTS (GNU/Linux 3.13.0-24-generic i686)）。 and then I want to update my kernel but after I updated I am checking by typing

uname -a

I got this:

3.13.0-24-generic

I do the update again and I got this:

linux-image-generic is already the newest version (4.15.0.163.152).

here is the message:

root@nordenbox:~# apt-get upgrade linux-image-generic 
Reading package lists... Done 
Building dependency tree        
Reading state information... Done 
  linux-image-generic is already the newest version (4.15.0.163.152).
Calculating upgrade... Done
0 upgraded, 0 newly  installed, 0 to remove and 0 not upgraded. 
root@nordenbox:~# uname -r
3.13.0-24-generic

I am confused. I am new to Linux and do these jobs on my VPS via SSH. and the CPU of my SVR is the 32-bit CPU.

root@nordenbox:~# update-grub
Sourcing file `/etc/default/grub'
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-5.4.0-91-generic
Found initrd image: /boot/initrd.img-5.4.0-91-generic
Found linux image: /boot/vmlinuz-4.15.0-163-generic
Found initrd image: /boot/initrd.img-4.15.0-163-generic
Found linux image: /boot/vmlinuz-3.13.0-24-generic
Found initrd image: /boot/initrd.img-3.13.0-24-generic
done