How to enable imagemagick?

I have both gd and imagemagick installed on my system but I can't work out how to switch to imagemagick. Any ideas? I upgraded from a previous version and it didn't give me the option in the setup and I can't find it in the options.

Also is imagemagick faster than GD for thumbnail generation on their install?

Information from php -i:
imagick

imagick module => enabled
imagick module version => 2.1.1-rc1
imagick classes => Imagick, ImagickDraw, ImagickPixel, ImagickPixelIterator
ImageMagick version => ImageMagick 6.5.7-8 2009-11-26 Q16 http://www.imagemagick.org
ImageMagick copyright => Copyright (C) 1999-2009 ImageMagick Studio LLC
ImageMagick release date => 2009-11-26
ImageMagick Number of supported formats: => 202
ImageMagick Supported formats => 3FR, A, AI, ART, ARW, AVI, AVS, B, BGR, BMP, BMP2, BMP3, BRF, BRG, C, CAL, CALS, CAPTION, CIN, CIP, CLIP, CMYK, CMYKA, CR2, CRW, CUR, CUT, DCM, DCR, DCX, DDS, DFONT, DJVU, DNG, DOT, DPX, EPDF, EPI, EPS, EPS2, EPS3, EPSF, EPSI, EPT, EPT2, EPT3, ERF, EXR, FAX, FITS, FRACTAL, FTS, G, G3, GBR, GIF, GIF87, GRADIENT, GRAY, GRB, GROUP4, HALD, HISTOGRAM, HRZ, HTM, HTML, ICB, ICO, ICON, INFO, INLINE, IPL, ISOBRL, JNG, JP2, JPC, JPEG, JPG, JPX, K, K25, KDC, LABEL, M, M2V, M4V, MAP, MAT, MATTE, MIFF, MNG, MONO, MOV, MP4, MPC, MPEG, MPG, MRW, MSL, MSVG, MTV, MVG, NEF, NULL, O, ORF, OTB, OTF, PAL, PALM, PAM, PATTERN, PBM, PCD, PCDS, PCL, PCT, PCX, PDB, PDF, PDFA, PEF, PFA, PFB, PFM, PGM, PGX, PICON, PICT, PIX, PJPEG, PLASMA, PNG, PNG24, PNG32, PNG8, PNM, PPM, PREVIEW, PS, PS2, PS3, PSD, PTIF, PWP, R, RADIAL-GRADIENT, RAF, RAS, RBG, RGB, RGBA, RGBO, RLA, RLE, SCR, SCT, SFW, SGI, SHTML, SR2, SRF, STEGANO, SUN, SVG, SVGZ, TEXT, TGA, THUMBNAIL, TIFF, TIFF64, TILE, TIM, TTC, TTF, TXT, UBRL, UIL, UYVY, VDA, VICAR, VID, VIFF, VST, WBMP, WMF, WMV, WMZ, WPG, X, X3F, XBM, XC, XCF, XPM, XPS, XV, XWD, Y, YCbCr, YCbCrA, YUV

Directive => Local Value => Master Value
imagick.locale_fix => 0 => 0