Hi Donna,
I would suggest that you stick to the 7th edition. The reason being is that the 6th edition, although still important, is no longer a focus for the PMP exam. I understand that prior to the change to the 7th edition, the ITTOs would form majority of the exam, but after PMI made changes in 2021 to the exam and the PMBOK got updated to the 7th edition, the 6th edition is no longer relevant. The concepts are very much still used and as a PM it is important that you know them, but if we are strictly speaking about the PMP exam, the 7th edition is the way to go. All that said, please keep in mind that the exam is not a test of the PMBOK, so you still need to expand your studies and touch on some other reference materials. I encourage you to read some of the latest lessons learned that are posted in this forum. Hope this helps, and all the best in your studies.
Regards,