I think it´s very easy thing to do,you just have to get rid of the rest of the glue in the backings(it they aren´t new of course)and if you have correct refills,they should fit without any problems.The trick you might be looking for is that you insert one end of the refill first(not all the way in though)and than you push the other end in.If you can´t push them all the way in like this,just put them in the vice,job done.With proper backings/refills you don´t even need to use a glue(I myself don´t use any),but if you´re worried,any superglue will be good,just don´t use too much of it.