igus has released a video that shows how easy it is to change an e-spool spring. The integrated retaining spring guides numerous cables round one roller at the precise length and retraction tension required. The tension on the spring can be tightened or slackened without removal by rotating the adjustment wheel either clockwise or anticlockwise.
Sometimes, for heavier loads applications, a higher power spring may be required. This can be achieved easily using standard igus tools and following the instructions in the video: www.igus.co.uk/e-spoolSpringExchange.