Quit LR4 and make a backup.
Download and install Creative Cloud on the MBP. Use this link. CC Desktop is your central management control for all of the CC apps.
I would suggest you install Photoshop CC 2015 first, followed by Lightroom CC 2015. Simply click on the install button next to each app.
You should be able to choose to upgrade your existing catalog. It will then be transferrable to the iMac.
Install CC Desktop on the iMac from the same link.
You will then need to copy the image files, previews and catalog to the iMac. See the link below – video tutorial - Moving to a new computer.
If you follow this procedure you get the benefit of ensuring everything works properly on the laptop before transferring to the new iMac.
Jon has you pointed in the right direction for installing the software on both computers.
One of the things to keep in mind is that Lightroom is a single-computer, single-user system. If you are wanting to "share" your catalog and images between computers, your best bet is to put the catalog and images on an external drive and move the drive from computer to computer as needed. There is no "sync" between computers.
Thank you so much for your help.
I have successfully purchased, downloaded and installed Lightroom CC 2015 and Photoshop CC 2015 on my MBP and my iMac.
It wasn't nearly as painful as anticipated.
Thanks for your advice and support. This was my first time asking a question in a forum and it was a good experience.
Thanks for your advice ManiacJoe, I have everything successfully downloaded on both computers.
I backed up my catalog to my external hard drive where I have all of my photos (yes, everything is backed up to a 2nd external hard drive) and I will take time tomorrow evening moving what I wish to work on into Lightroom and continue on with my editing!
All your images should still be in your LR catalog, no need to "move" anything.
When you start LR6, point it to your LR4 catalog. LR6 will migrate your data to the new LR6 format catalog with a "-2" appended to the catalog name.
Since you are creating a new catalog with LR6, you be creating a new set of preview files; so this may take some time (in the background).
When I installed LR6 on my MBP it did load my catalog back up and everything is there ... whew!
I will try migrating my data to my iMac. Thanks for the info about the appended catalog name. This is where I will be doing the majority of my work.
Will I be able to back up my catalog yet again on my external and migrate the latest back up to my MBP or will that become too confusing?
I use my MBP when on vacation. Then import the on-location catalog to the master catalog on the desktop machine. It may work for you.
Here is a good video tutorial from Adobe TV.
Lightroom is a single-computer, single-user system. To "share" a catalog between computers takes some tricks.
Putting your catalog and photos on an external drive and moving the drive from computer to computer is the easiest way to go as there is no sharing at that point.
Using a temporary "On Location" catalog then "importing" that catalog into the main catalog is the second approach as outlined in Jon's video link.
I followed your first recommendation and added my catalog to my iMac by using my external hard drive. Again, success.
When I installed LR6 on my MBP I set that up as the place to connect to my mobile devices. I would prefer to use my iMac for that purpose as it will be my primary computer. How do I make that change?