How do you calculate its magnitude please ?
This is not an easy question to answer! I would recommend reading the AAVSO photometry guide which is kept well up to date:
As to the choice of software, I can personally recommend the Tycho Tracker software. The Pro version is well worth the $50 for the licence and is very easy to get going with. There are plenty of YouTube videos to get you started. Many will say to use AstroImageJ (which is free) but I think this is hard to get going with. I also use the amazing (and underrated) AstroArt8 software which is easily scriptable.
https://www.tycho-tracker.com/
Hope that helps.
Ian