Moving/resiting oil tanks yourself is a foolish idea, get a qualified Oftec registered installer to do it for you.
If you do this incorrectly (and I bet 99.99% you will as you do not know the regs that govern it) and in the future your tank sheds it load (happens so much more often than you think!) you insurance company will not cover you, and the cost of the cleanup usually runs between €9000 - €15000 for removal of the surrounding soil as toxic waste, and thats about the best case, if there is open water source and it goes in there, you could be facing huge costs........it's not worth it
Considerations, are location, fire rating, support, foundations, and much more..........