Updating information in working memory is a critical process which makes possible to have available, at every moment, the information most relevant for mind operations. However, the specific mechanisms underlying the updating process have rarely been analysed. This paper examines the importance of two of the mechanisms implicated in a numerical updating task: item comparison and item substitution. The item comparison mechanism was studied by manipulating the size distance between items. The item substitution mechanism was investigated by increasing/decreasing the number of updates within trials. Furthermore, in order to examine the effects of time constraints, presentation rate was manipulated. Over three experiments, the results obtained highlighted that updating performance is mainly influenced by suppression request, even when the presentation rate is self-paced. However, errors depend on the distance between items. The implications of the results for the understanding of updating are discussed.