Individual differences in serial versus parallel processing of multiple tasks are well documented, yet the extent to which they can be altered by training remains unclear. To address this, we use the task-switching with preview (TSWP) paradigm to examine whether preferred processing modes in task-switching can be modified with training and how such changes influence multitasking efficiency. In TSWP, two tasks alternate every three trials, with the currently irrelevant task’s stimulus (preview) remaining visible, allowing for task pre-processing. The key result from TSWP is that some individuals process the preview in parallel, achieving frequent fast switches and corresponding switch benefits, whereas others opt for serial processing. Our currently ongoing training study comprises five sessions: Sessions 1 (Pre-Test) and 5 (Post-Test) include TSWP training and a transfer TSWP test using a different set of stimuli, while Sessions 2-4 consisted of TSWP training only. The preliminary analysis based on N = 20 participants (goal sample size N = 40) currently suggests an overall increase in fast switch rates across sessions, reflecting a shift toward overlapping processing. This effect is also evident in the transfer test data, indicating stimulus-independent improvements and generalization to new tasks. We additionally included pre- and post-measures of working memory capacity and fluid intelligence to explore their relationship with processing mode changes. The final results of this first experiment will be discussed, along with the design of a follow-up experiment where we will explicitly instruct individuals to process the tasks either in a more serial or parallel way.