Only upgrade by means of installing a new complete firmware image (i.e. 19.07.0 > 19.07.1) using the sysupgrade functionality.
The images (and packages from that build cycle) are all self-consistent in terms of kernel versions and dependencies. Performing an
opkg upgrade operation will likely break things -- there are no advanced compatibility checks in the package manager to ensure that everything will continue to work.
See this link and search the forums for the number of times that people have broken their installations by using the
opkg upgrade command. It is never advisable to upgrade this way, but if you absolutely must have some specific bug fix or new feature or something, be sure to do this very carefully, selectively, and with the complete knowledge that you may soft-brick your router in the process (most of the time it is recoverable by booting failsafe mode and then performing
firstboot to reset everything to defaults).