The rules for the MEP Selection Meetings for the 2014 European Elections have a clause saying:
Agreement of 60% of those present at the meeting should be required for re-adoption.
If an MEP is not re-adopted they will have the right to be included in the postal ballot of party members alongside new applicants.
To be a wholly democratic process the existing MEPs should be judged alongside the new applicants so do not vote for an existing MEP and let Party members decide in a ballot of all candidates. That is the democratic way to do it and it gives the party members the dignity of real choice of all the candidates.