You can probably re-wire them by removing the resistors, but you'd probably need to re-calculate the resistor needed (if any) depending on the number of LED's you want to use.
The main thing you need to remember is that the current will drop across each LED, so for example if your current LED + resistor is calculated to provide say 100ma, by putting two in series with the resistors in place may drop the amount of current getting to each LED to between 50 to 10ma as the effect is likely to be cumulative. This will result in the LED losing brightness and eventually may drop below the threshold to light them at all.
The other thing to remember is the connections are polar (i.e. negative and positive) get it round the wrong way and they won't work at all lol!
The main thing you need to remember is that the current will drop across each LED, so for example if your current LED + resistor is calculated to provide say 100ma, by putting two in series with the resistors in place may drop the amount of current getting to each LED to between 50 to 10ma as the effect is likely to be cumulative. This will result in the LED losing brightness and eventually may drop below the threshold to light them at all.
The other thing to remember is the connections are polar (i.e. negative and positive) get it round the wrong way and they won't work at all lol!
Happily collecting things all my life... 
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