Update Qt library/creator; using old projects? (Mac)

[badmilk101]

Note: I am still very much a beginner when it comes to programming and using programming tools. My OS is Mac OS X 10.8.4.

For the past couple years, I had used Qt Creator 1.?.? based on the Qt 4.6.? library to create some very basic programs (think "Hello World", Tic-Tac-Toe", etc.). [question marks are there because I don't recall the versions exactly].

I recently found the need to use a more recent version of the Qt library (version 4.8). I downloaded and installed Qt libraries 4.8.5 for Mac (but not the debug libraries). I then downloaded Qt Creator 2.7.1 for Mac and dragged it to my Applications folder, which replaced [deleted] my previous version of Qt Creator.

I have tried various settings for "configure project" for my old projects, but I can't get any of them to compile. They all give errors referencing a "version 4.6", which seems bad. Here is the type of thing I get...

17:28:09: Starting: "/usr/bin/qmake" /Users/my_username/Qt_stuff/NNNcube2/NNNcube2.pro -r CONFIG+=x86_64 -spec /usr/local/Qt4.6/mkspecs/macx-g++
Failure to read QMAKESPEC conf file /usr/local/Qt4.6/mkspecs/macx-g++/qmake.conf.
Error processing project file: /Users/my_username/Qt_stuff/NNNcube2/NNNcube2.pro
17:28:09: The process "/usr/bin/qmake" exited with code 3.
Error while building/deploying project NNNcube2 (kit: Qt 4.8.4 in PATH (System))
When executing step 'qmake'

17:28:09: Starting: "/usr/bin/qmake" /Users/my_username/Qt_stuff/NNNcube2/NNNcube2.pro -r CONFIG+=x86_64 -spec /usr/local/Qt4.6/mkspecs/macx-g++
Failure to read QMAKESPEC conf file /usr/local/Qt4.6/mkspecs/macx-g++/qmake.conf.
Error processing project file: /Users/my_username/Qt_stuff/NNNcube2/NNNcube2.pro
17:28:09: The process "/usr/bin/qmake" exited with code 3.
Error while building/deploying project NNNcube2 (kit: Qt 4.8.4 in PATH (System))
When executing step 'qmake'

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1. Did I update Qt Creator & Qt library incorrectly? If so, what should I have done?

2. Am I naive/ignorant to think that I should be able to update from 4.6 to 4.8 without too many issues? Should I have instead tried to keep my old instance of Qt Creator (w/4.6 lib.) and created a new instance of Qt creator (w/4.8 lib.)?

3. What should I do now to remedy the situation (to be able to use my old projects)? None are terribly important, but it would be nice to have them.

Thanks!