Will it would be possible to switch project types. Going from multiple suites to a single repository would require you to consolidate test cases you wish to keep into a single suite, then delete the extra suites. Keep in mind you would need to close any open runs first to retain their test case configuration and test result history.
Alternatively, a less destructive method would be to copy the test cases into a new project. It would be possible for you to simply copy or move your test cases from one suite/project to another in order to reuse the test cases you have used in other projects and you would accomplish this via the Copy & Move dialog. You would simply navigate to the destination project, click the Copy or Move Cases icon at the top right corner of the test case suite, choose the project that is the source of the test case(s) you would like to copy from, and then specify the cases you would like to copy and you can find more information about this here:
Please note that this won’t move any test results though and if you move test cases to another suite rather than copying them this will delete any test results of any not-yet closed runs using the source test suite.