Thats good all is fine with your upgrade.
Did you download and install the 7Zip program?
If you have the program you can open and check the archive and manually extract the files to a directory of choice if the self extracting process leaves you with no control.
A quick and nasty backup method I use is just to Ctrl/drag the xampp directory to make a copy of xampp
Then if the ugrade is ok I delete the copy of xampp
If I have to revert then I delete the errant xampp and rename the copy of xampp
back to xampp.
Just to add, as a general rule, upgrades usually only replace by over-writing core files and by adding files if need be. It does not delete files or add or change any configuration files.
If the contents of an upgrade are checked it will be seen that no configuration files are included in the archive.
When core files have to be deleted and configuration files upgraded/changed there is no upgrade just a new version install.
IIRC, the version 1.5.4 was one of those non upgradeable version releases.