Am I mistaken or is 4.5 PU8 just the **minimum** level you can go to 2018 with?
See prior conversation for more discussion;
https://90minds-com.socialcast.com/messages/37376643?ref=stream
In other words, you could also upgrade to 2017 and then to 2018 as well. @BillPfahnl keeps a ZIP of a 2017 standard which he copies to the server and uses to migrate. Note, it appears that if you have 2018 already installed that Sage balks at letting you install 2017 as well which is why Bill's procedure may be faster as you can copy/paste and fire up 2017 without an install routine and presumably without knocking heads with 2018.
IIRC, some people have asked specifically for 4.5 PU8 because they had customers on 4.5 and did not / could not make a full version jump due to enhancement issues.
Please correct if wrong as I'm about to embark on a 4.4 to 2018 and I was preparing to follow Bill's lead and go 2017 with a ZIP install then 2018.