Mdtryhht

Assumed we have this MWE from user Caramdir:

documentclassarticle
usepackagetikz
usetikzlibraryarrows,calc,decorations.markings,decorations.pathmorphing,arrows.meta

begindocument
begintikzpicture
 draw [domain=0:25.1327,variable=t,smooth,samples=75, -Latex]
 plot (t r: 0.002*t*t);
endtikzpicture
enddocument

I want to reverse the arrow head position, so that the arrow tip is located at the inner end of the spiral and directs to the center.

How to do so?

To have arrow's head on opposition side of the spiral curve, you only need to change -Latex to Latex-. However result is quite unexpected (read unusable) ...

It might be more acceptable solution to move the arrow head close to the end of the spiral. For this you can exploit the package decorations.markings:

documentclass[tikz, margin=3mm]standalone
usetikzlibraryarrows.meta, bending, decorations.markings

begindocument
 begintikzpicture[
decoration = markings,mark=at position .84 with
 arrowreversed[black]Latex[length=1.5mm]
 ]
draw[postaction=decorate]
 plot[domain=0:25,variable=t,smooth,samples=101,
 Latex[length=1mm]-]
 (t r: 0.002*t*t);
endtikzpicture
enddocument

First of all, I would like to argue that bent arrows look better, also in the original plot. But since the curve becomes singular at 0, this does not immediately work because of dimension too large errors. However, it does once we approximate the inner-most stretch by an arc.

documentclassarticle
usepackagetikz
usetikzlibraryarrows.meta,bending

begindocument
begintikzpicture[scale=2]
 pgfmathsetmacromytpi 
 draw[Latex[bend,length=2pt]-] 
 (0: 0.002*myt*myt)
 arc(0:180:0.002*myt*myt);
 draw plot[domain=pi:25.1327,variable=t,samples=75,smooth]
 (t r: 0.002*t*t);
endtikzpicture
enddocument

And here is the original pic with a bent arrow.

documentclassarticle
usepackagetikz
usetikzlibraryarrows.meta,bending

begindocument
begintikzpicture
 draw [domain=0:25.1327,variable=t,smooth,samples=75, -Latex[bend]]
 plot (t r: 0.002*t*t);
endtikzpicture
enddocument

Note that one should always load bending when one attaches arrows to curved paths, regardless of whether or not one bends the arrows, since otherwise the paths get distorted. Bending cures the distortion even when not explicitly used.