Step 1: Install the MolecularShell using the HENKaku exploit by watching this video here,
If you've already done this, skip to step 2
Step 2: Download VitaShell.vpk from above and open up your MolecularShell and be sure that the Unsafe Homebrew environment is enabled/switched to ON. how to do that is simply hit the START button on your Vita while in MolecularShell and turn the option to ON. Once that's done, exit and reboot the application and you will see more folders available.
Step 3: Activate the FTP client on the Vita by hitting the SELECT button with the application open and you will see an IP address pop up kinda like this "ftp://22.214.171.124:1234" what ever that says is what is going to be copied to your PC for file transfer.
Step 4: On your PC navigate to My Computer, Computer or This PC depending on witch version of windows your running and right click on the blank space and select "Add a network location" the wizard will open up and just select "Next" then select "Choose a custom network location" and hit Next. You will be asked to input an IP and that's where you will copy your "ftp://126.96.36.199:1234" or whatever your numbers are in that slot. Proceed with the process and you can rename the connection if you want.
Step 5: Once completed, you can now access your Vita with your FTP client, if you click on the connection you just made you will see your files on your Vita, we are going to navigate to ux0:/
Step 6: Navigate to the directory "ux0:/VitaShell" now just copy the VitaShell.vpk to this folder.
Step 7: On the Vita in your MolecularShell navigate to that same folder and press X on the package and it will prompt you for install, hit X again and your done.
NOTE: I recommend using VitaShell for bigger files for transfer because MolecularShell runs into problems transferring large files but for installing small VPK files its fine.