One of the hardest concepts to get your head around when playing with computers is that you buy a software licence to run programs. You do not "own" the software. You buy the right to run the software. This is difficult to get your head around, for most people, because they have a CD-ROM or DVD with the software on it and possibly a set of manuals. So it is only natural to think you have physical ownership. Nothing is further from the truth.
If you read through the hundreds of pages of user licence agreements couched in dense legal prose and six point sans serif font, you will discover that it is all designed to present the fact that you have been granted very limited rights to run the software and the software manufacturer may withdraw that right or support on any or no reasons at all.
The easiest way to get around these registration issues is having the foresight to make copies of all the registration details in the first place. There are several programs available that will search through your computer and identify the software licence codes. Some even work after problems have arisen, but the key point is that you need to be prepared before problems start.
Before doing any upgrades or modifications, run one of these software licence details capture programs and print off the results.
A little knowledge is a dangerous thing when it comes to computers. I started out building my first computer from scratch using discrete components and loading and saving programs from an audio cassette tape. I regard myself as being pretty computer literate but I still frequently get caught out by hardware and software issues.