我正在尝试从 18.04 升级到 20.04，但收到错误消息：
Could not calculate the upgrade
An unresolvable problem occurred while calculating the upgrade.
This was likely caused by:
* Unofficial software packages not provided by Ubuntu
Please use the tool 'ppa-purge' from the ppa-purge
package to remove software from a Launchpad PPA and
try the upgrade again.
If none of this applies, then please report this bug using the command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal. If you want to investigate this yourself the log files in '/var/log/dist-upgrade' will contain details about the upgrade. Specifically, look at 'main.log' and 'apt.log'.
我已经看过主日志和apt.log，但我的 Ubuntu 技能不够好，无法理解它们，而且我不确定是否可以删除所有损坏的软件包。