1st off,get yourself a bag of Perlite! Available from any garden centre,mix it with your new soil about 40% Perlite.Then take your plant,stem between your fingers and turn upside down,gently tap out the plant,then gently remove all compost that DOESN`T have roots in it,bit of your new mix in the pot to bring the plant up to height(you can bury a bit of your stem)then back fill and firm-jobs a good ùn.Just a few tips.... that looks like over watering to me,its better to water little and often than soaking and waiting 3/4 days to dry out,also dont use too big a pot as your plants wont be able to use up the water and will get oxygen starved and root rot-your roots need air.
Peace RM.