1 want to change my garage door and put window there what do ido?

Do it, if its anything like my garage used to be then its chocker with junk & no room for the car for which it was intended! I changed mine about 10 years ago and its now a fully functional room which is in constant use & a very valuable addition to the accomodation. When I did mine I had to get planning permission, but I dont think you need it now, but obviously you need to comply with building regulations. Its not hard ( if you are reasonably handy) Apart from building the wall I did the lot myself & think the whole project cost less than 2K incl. plastering, building, electrics. heating & decorating & if its done well will be really worthwhile..........Good luck with it