Navigate to Start and type diskmgmt.msc in the search bar. Press Enter.
Disk Management opens. You should find your Drives listed including removable devices. Right click the USB drive (in our case /E:) and select Change Drive Letter and Paths.
The Change Drive Letter and Paths dialog box appears for the selected drive displaying the current drive letter. Click Change.
In the Change Drive Letter or Paths dialog box, select the Assign the following drive letter radio button. On the drop down list to the right, select a letter between M and Z (preferably). Click OK to continue.
A warning message pops up stating that some programs that rely on certain drive letters may not function properly. Click Yes.
The new drive letter (in our case \P:) appears next to the drive in Disk Management. Exit out of Disk Management.
From now on, absolute file paths will not have to be amended for particular programs such as back up programs, every time you connect up your USB drive.