Our previous work on improving the quality of objectoriented legacy systems includes : i) devising a qualitydriven re-engineering framework [11], ii) proposing a software transformation framework based on soft-goal interdependency graphs to enhance quality [9], and iii) investigating the usage of metrics for detecting potential design flaws [10]. This paper defines a decision making process that determines a list of source-code improving transformations among several applicable transformations. The decisionmaking process is developed on a multi-objective decision analysis technique. This type of technique is necessary as there are a number of different, and sometimes conflicting, criterion among non-functional requirements. For the migrant system, the proposed approach uses heuristic estimates to guide the discovery process.