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I have tried following similar questions but nothing is helping. when I try to install I get the error "an unresolvable error occured while calculating upgrade "
Unresolvable errors usually mean non-Ubuntu packages from PPAs and other non-Ubuntu sources. Return the packages on your system to as close to stock condition as possible. Look up how to use the ppa-purge command to accomplish it.
If you attempted do-release-upgrade from terminal you get lots of messages which indicate the problems (messages are above that summary you mentioned. We can advise if you provide such messages but cannot offer more given what you've provided. user53733 has already stated your likely cause. One easy option is to backup, download the 18.04.2 ISO & write to install media, verify it (an option before the try/install question) then install using 'something else' & using no FORMAT (careful). All system directories are deleted, 18.04 installed & your added software (from Ubuntu repos) re-added
It is so much better to do a fresh install, i.e. installing while whipping out the old install. Then you start with a clean slate and eliminate any risk or contamination from old configuration data and settings.
ppa-purge
command to accomplish it.do-release-upgrade
from terminal you get lots of messages which indicate the problems (messages are above that summary you mentioned. We can advise if you provide such messages but cannot offer more given what you've provided. user53733 has already stated your likely cause. One easy option is to backup, download the 18.04.2 ISO & write to install media, verify it (an option before the try/install question) then install using 'something else' & using no FORMAT (careful). All system directories are deleted, 18.04 installed & your added software (from Ubuntu repos) re-added