Help with pruning tree!?

My landlady asked a while ago if I could lop the top of a tree off that we have in the garden. I forgot all about it until now!

Do I just chop the top off?
Is it the right time to do it?

Here's the tree in question;

 

It seems a shame to do it but if that's what your landlady wants.....

Leave the tree until it's fully dormant. While it still has leaves on it the sap is still dropping. I'd leave it another month. How much does she want taken off?

 

Thanks both.

Armandii, she wanted around a 3rd lopped off funnily enough. I shall set about it within the next week or so then.

 

Does anyone think it looks like a cherry?
Prunus?

If so it should be pruned in summer to avoid silverleaf disease.

https://www.rhs.org.uk/advice/profile?pid=245

 

Thats just what I was thinking.
If you prune it now you wont have to worry about future growth because it will die from silverleaf.
To be honest it looks like it will never grow into a nice shaped tree as there are too many trunks already on it and chopping the top off will just give another mass of side shoots making it look a hole lot worse.
To be honest Id get a new tree bud.

 

I'm not quite sure that silver leaf is a cert if you prune now, but I do think it is a possibility.

And the tree is a very bad shape.
I'd be interested to know if it flowered last spring?

Just wondering if we are mostly looking at rootstock growth?

 

Cherry tree. Prune in the summer to avoid possible silver leaf infection. Reduce in height with neat cuts from a sharp, clean pair of secateurs, cut out the whippy stems at the base.