There is a config file that stores everything. You just need to back that up. On Windows 7 it resides in
C:\Program Files (x86)\FinalWire\AIDA64 Extreme Edition\aida64.ini
If you are on another version of windows and can't find it, just search your windows install drive for aida64.ini and you should be able to find it easy enough. Save this file before you uninstall, then after you reinstall, just overwrite the new file with the one you backed up. This file includes all of your LDC Items Settings (to access from AIDA64, click File > Preferences then navigate to LCD > LCD Items. All of the Items, BMP's and Labels you setup there get stored to the aida64.ini file.
As a side note, if you are currently using Everest, the software and file structure is pretty much identical, so if you are converting over from Everest to AIDA64 and have already setup some LCD Items in Everest, just find your everest.ini file, back it up or save it somewhere, uninstall Everest, then install AIDA64. After you install AIDA64, rename your everest.ini file to aida64.ini and overwrite C:\Program Files (x86)\FinalWire\AIDA64 Extreme Edition\aida64.ini with the renamed file.
Hope that makes sense...here is another thread on this topic if you want to read more
If you paid for an Everest license, you can transfer it to AIDA64 (or at least I was able to...don't know if that is a limited or temporary offer, but you should jump on it sooner rather than later if you are a current Everest user)