For long-lived systems, there is a need to address evolvability (i.e. a systems ability to easily accommodate changes) explicitly during the entire lifecycle. In this report, we undertake a systematic review to obtain an overview of the existing studies in promoting software evolvability at architectural level. The search strategy identified 3036 studies, of which 54 were catalogued as primary studies for this review after using multi-step selection process. The studies are classified into five main categories of themes, including techniques that support quality considerations during software architecture design, architectural quality evaluation, economic valuation, architectural knowledge management and modeling techniques. Four dimensions of factors are identified that exert influence on software evolvability. To cope with these diverse influencing factors, combination of appropriate techniques becomes necessary.