Upgrading the kernel for Debian unstable/testing is very easy.
Upgrading the kernel for Debian stable is very hard, basically only when there is a newer version in the backport repository. However, if you want to upgrade to a even newer kernel, you would probably have to do what I said. Try to install a copy of Debian stable (4.19 kernel) and try to upgrade it to 5.7 and see what happens.
