Updated Lightoom and cannot "link" or access ircat libraries

I just updated Adobe Lightroom and cannot get my photos to open. Let me know if there is a way to get Ligthroom to simply open my "old" libraries. I have followed tutorials on line but many of these suggest features that I do not see such as: File>Open Catalog. If I use the "add photos" option, I can see the masters but the program believes that I want to essentially duplicate these and responds with "insufficient memory" (needing 16GB). The only way I can think to solve this problem is to get an external hardrive and copy the photos and then delete the old library. I would appreciate any help.