Large amounts of space taken up on my C + D drives

Having had a few problems with my PC recently I seem to have got them sorted out now. However, using one of these Tree Directories (Windirstat) I seem to have some large amounts of disk space taken up by various things. (see various photos). What I’m asking is whether I can safely delete some of these or reduce their size? My drive is split into C: for system and D: for data and they are getting quite full now.

Under Windows \ System32 I see a greyed out folder called Memory.DMP – do I need that?
Under WinSXS I have 11 gb of stuff – do I need all of that or can I delete??
Under Users there is a folder of Appdata showing 16gb. Is this all really needed stuff??
System error dump files seems to hold 2gb. Needed?
On my data drive D: I have found that there is a pagefile.sys of 16gb which has mysteriously found its way to being a subfolder of my Photos folder. (I thought pagefile.sys was supposed to be somewhere on C:). Can I safely reduce its contents and somehow transfer it back to C: drive ?

All other large size folders contain films, music etc and safety image backup copies so I can decide myself whether to keep them or delete/transfer.
So, any advice on how I can claw back any space on drives will be appreciated.