It depends on whether the new version of LR uses a new catalogue format, a new preset format etc.
If it's all the same format, it just carries on working with your existing catalogue, presets etc.
If the new version has a new catalogue format, then what probably happens is that first time you run it (the release version LR5, not the beta) it will copy your existing catalogue into a new one in the new format, probably converting all your presets too.
I expect it will work with or convert all your existing stuff, or warn you of anything that doesn't convert.