If you have a second empty hive, put the new package in there.
If you don’t, I would put the new package in an empty lower brood box after checking that the queen is alive and well (they are usually caged, so that is easy). Put the new queen in with them. Kill the old package queen. Put the old package bees in a box on top of the new package, but with a double layer of newspaper between them. Leave some food in the old package box as a bribe to get the new bees up there and make them less likely to fight the old package.
As soon as they have merged (2-5 days), condense them back down to one box and feed as necessary while they get established.
Sorry that beekeeping can be complicated, but that is life sometimes! 