What are the steps to take if I want to respray the tank using aerosol paint from...
 

...DIY shop? Is it posible to achieve good quality result,or I'll be better off if I take it to the garage? Thanks

what tank an no u won't get a professional look You have to do the same no matter what u paint sand it clean it of all oil an grease than do several layers not just one coat

Tanks get hot, and this will cause paint to peel if not done professionally. If there is maybe a plastic part to the tank you can spray just that, but be VERY careful when cleaning or chemicals will ruin the paint job. If it is a solid metal covered tank spray paint is a definite no.