Just don't use it.... seriously, don't. Unless you know exactly what you are doing, or are willing to deal with the consequences of messing up your router (and having to start over completely). The 'problems' you are experiencing attempting to use opkg upgrade are very likely saving you from major problems on your router!
The fact that you are not familiar with the arguments for the upgrade command further reinforces that you should not be using it. However, if you are looking to upgrade your OpenWrt version (say from 19.07.1 > 19.07.2), that is easy using the sysupgrade command.